Semiconductor device

ABSTRACT

There is provided a technology which allows improvements in manufacturing yield and product reliability in a semiconductor device having a triple well structure. A shallow p-type well is formed in a region different from respective regions in a p-type substrate where a deep n-type well, a shallow p-type well, and a shallow n-type well are formed. A p-type diffusion tap formed in the shallow p-type well is wired to a p-type diffusion tap formed in a shallow n-type well in the deep n-type well using an interconnection in a second layer. The respective gate electrodes of an nMIS and a pMIS each formed in the deep n-type well are coupled to the respective drain electrodes of an nMIS and a pMIS each formed in the substrate using an interconnection in a second or higher order layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2008-123634 filed onMay 9, 2008 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor device and, moreparticularly, to a technology which is effective when applied to asemiconductor device formed with a well in a three-layer structure,i.e., a so-called triple well structure which has a deep well of asecond conductivity type different from a first conductivity type in asubstrate of the first conductivity type, and further has a shallow wellof the first conductivity type in the deep well.

For example, Japanese Unexamined Patent Publication No. 2006-303753(Patent Document 1) describes a logic circuit and an I/O circuit in asemiconductor integrated circuit device having a so-called triple wellstructure. In the triple well structure, a deep n-well is formed on ap-type semiconductor substrate, and an n-well for forming a p-typeMISFET and a p-well for forming an n-type MISFET are formed thereon.

Japanese Unexamined Patent Publication No. Hei 11-97560 (Patent Document2) discloses a technology which forms, in a nonvolatile semiconductormemory device having a floating gate electrode and a control gateelectrode on a semiconductor substrate, an n-well in a p-typesemiconductor substrate, forms a p-well in the n-well, forms anantistatic n-type diffusion layer in the p-well, and electricallycouples the antistatic diffusion layer and the control gate electrode toprevent the degradation of the reliability of an insulating film due tocharging during the processing of an interconnection layer by etching,or prevent a dielectric breakdown therein.

Japanese Unexamined Patent Publication No. 2005-340548 (Patent Document3) discloses a technology which couples a floating interconnection to aclamp diode to transfer charge that has flown to the floatinginterconnection to the clamp diode, and thereby prevent a short circuitbetween the floating interconnection and a ground interconnectionadjacent thereto.

Japanese Unexamined Patent Publication No. 2001-358143 (Patent Document4) discloses a technology for a semiconductor device including at leastone interconnection layer including a plurality of relay pinselectrically coupled to a plurality of respective gate electrodes, andan uppermost interconnection layer including a plurality ofinterconnection patterns which are electrically coupled to the pluralityof respective relay pins. According to the technology, the gateelectrodes are wired using the uppermost-layer interconnection patternto transfer electrification charge to a region other than the gateelectrodes during the etching of the interconnection layers, and therebyprevent the degradation of gate insulating film.

[Patent Document 1] Japanese Unexamined Patent Publication No.2006-303753 [Patent Document 2]

Japanese Unexamined Patent Publication No. Hei 11-97560

[Patent Document 3] Japanese Unexamined Patent Publication No.2005-340548 [Patent Document 4] Japanese Unexamined Patent PublicationNo. 2001-358143 SUMMARY OF THE INVENTION

In a SOC (System On Chip) product, a semiconductor device having atriple-well structure is used for the purpose of reducing powerconsumption during standby or the like. However, the semiconductordevice having the triple-well structure has various technologicalproblems described hereinbelow.

In general, for signal transfer, electrical coupling is provided asnecessary between field effect transistors respectively formed indifferent triple well regions, and between a field effect transistorformed in a triple well region and a field effect transistor formed in asubstrate region. However, a study conducted by the present inventorshas revealed that, in a specified circuit, a dielectric breakdown due toa triple well structure occurs in the gate insulating film of a fieldeffect transistor. As an effective method for preventing such adielectric breakdown, a method can be considered which, e.g., provideselectrical coupling between field effect transistors respectively formedin different triple well regions via a level shift circuit. However, thelevel shift circuit has been originally designed to provide couplingbetween regions with mutually different power supply voltages. When thelevel shift circuit is disposed for each signal line between regionseach with the same power supply voltage, not only design is complicated,but also the level shift circuit occupies a partial region of asemiconductor device. Accordingly, the semiconductor is increased insize to cause a problem of higher product manufacturing cost or thelike.

An object of the present invention is to provide a technology whichallows improvements in manufacturing yield and product reliability in asemiconductor device having a triple well structure.

The above and other objects and novel features of the present inventionwill become apparent from the description of the present specificationand the accompanying drawings.

As shown below, a brief description will be given of an embodiment of arepresentative aspect of the invention disclosed in the presentapplication.

The embodiment (first method) is a semiconductor device having a deepn-type well formed in a p-type substrate, which includes a first shallowp-type well and a second shallow n-type well which are formed inmutually different regions in the substrate, a third shallow p-type welland a fourth shallow n-type well which are formed in mutually differentregions in the deep n-type well, an inverter circuit including ann-channel field effect transistor formed in the first shallow p-typewell in the substrate and a p-channel field effect transistor formed inthe second shallow n-type well in the substrate, and an inverter circuitincluding an n-channel field effect transistor and a p-channel fieldeffect transistor which are respectively formed in the third shallowp-type well and the fourth shallow n-type well in the deep n-type well.In a region different from the respective regions where the deep n-typewell, the first shallow p-type well, and the second shallow n-type wellare formed, a shallow p-type well is formed. A p-type diffusion tapformed in the shallow p-type well is wired to a p-type diffusion tapformed in the third shallow p-type well using an interconnection in ann-th layer. The respective gate electrodes of the n-channel field effecttransistor and the p-channel field effect transistor each formed in thedeep n-type well are wired to the respective drain electrodes of then-channel field effect transistor and the p-channel field effecttransistor each formed in the substrate using an interconnection in ann-th or higher order layer.

Another embodiment (second method) is a semiconductor device having adeep n-type well formed in a p-type substrate, which includes a firstshallow p-type well and a second shallow n-type well which are formed inmutually different regions in the substrate, a third shallow p-type welland a fourth shallow n-type well which are formed in mutually differentregions in the deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the substrate, and aninverter circuit including an re-channel field effect transistor and ap-channel field effect transistor which are respectively formed in thethird shallow p-type well and the fourth shallow n-type well in the deepn-type well. In a region different from the respective regions where thedeep n-type well, the first shallow p-type well, and the second shallown-type well are formed, a shallow p-type well is formed. An n-typediffusion layer formed in the shallow p-type well is wired to an n-typediffusion tap formed in the fourth shallow n-type well using aninterconnection in an n-th layer. The respective gate electrodes of there-channel field effect transistor and the p-channel field effecttransistor each formed in the deep n-type well are wired to therespective drain electrodes of the n-channel field effect transistor andthe p-channel field effect transistor each formed in the substrate usingan interconnection in an n-th or higher order layer.

Still another embodiment (third method) is a semiconductor device havinga first deep n-type well and a second deep n-type well each formed in ap-type substrate, which includes a first shallow p-type well and asecond shallow n-type well which are formed in mutually differentregions in the first deep n-type well, a third shallow p-type well and afourth shallow n-type well which are formed in mutually differentregions in the second deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the first deep n-type well,and an inverter circuit including an n-channel field effect transistorand a p-channel field effect transistor which are respectively formed inthe third shallow p-type well and the fourth shallow n-type well in thesecond deep n-type well. An n-type diffusion tap formed in the secondshallow n-type well in the first deep n-type well is wired to an n-typediffusion tap formed in the fourth shallow n-type well in the seconddeep n-type well using an interconnection in an n-th layer. Therespective drain electrodes of the n-channel field effect transistor andthe p-channel field effect transistor each formed in the first deepn-type well are wired to the respective gate electrodes of the n-channelfield effect transistor and the p-channel field effect transistor eachformed in the second deep n-type well using an interconnection in ann-th or higher order layer.

Yet another embodiment (fourth method) is a semiconductor device havinga first deep n-type well and a second deep n-type well each formed in ap-type substrate, which includes a first shallow p-type well and asecond shallow n-type well which are formed in mutually differentregions in the first deep n-type well, a third shallow p-type well and afourth shallow n-type well which are formed in mutually differentregions in the second deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the first deep n-type well,and an inverter circuit including an n-channel field effect transistorand a p-channel field effect transistor which are respectively formed inthe third shallow p-type well and the fourth shallow n-type well in thesecond deep n-type well. A p-type diffusion tap formed in the firstshallow n-type well in the first deep n-type well is wired to a p-typediffusion tap formed in the third shallow n-type well in the second deepn-type well using an interconnection in an n-th layer. The respectivedrain electrodes of the n-channel field effect transistor and thep-channel field effect transistor each formed in the first deep n-typewell are wired to the respective gate electrodes of the n-channel fieldeffect transistor and the p-channel field effect transistor each formedin the second deep n-type well using an interconnection in an n-th orhigher order layer.

Still another embodiment (fifth method) is a semiconductor device havinga first deep n-type well and a second deep n-type well each formed in ap-type substrate, which includes a first shallow p-type well and asecond shallow n-type well which are formed in mutually differentregions in the first deep n-type well, a third shallow p-type well and afourth shallow n-type well which are formed in mutually differentregions in the second deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the first deep n-type well,and an inverter circuit including an n-channel field effect transistorand a p-channel field effect transistor which are respectively formed inthe third shallow p-type well and the fourth shallow n-type well in thesecond deep n-type well. The semiconductor device further includes afirst diode including a sixth shallow p-type well and an n-typediffusion layer, and a second diode including a seventh shallow p-typewell and an n-type diffusion layer in mutually different regions otherthan respective regions where the first and second deep n-type wells areformed. The n-type diffusion layer forming the first diode is wired toan n-type diffusion tap formed in the second shallow n-type well in thefirst deep n-type well using an interconnection in an n-th layer. Then-type diffusion layer forming the second diode is wired to an n-typediffusion tap formed in the fourth shallow n-type well in the seconddeep n-type well using the interconnection in the n-th layer. Therespective drain electrodes of the re-channel field effect transistorand the p-channel field effect transistor each formed in the first deepn-type well are wired to the respective gate electrodes of the n-channelfield effect transistor and the p-channel field effect transistor eachformed in the second deep n-type well using an interconnection in ann-th or higher order layer.

Yet another embodiment (sixth method) is a semiconductor device having afirst deep n-type well and a second deep n-type well each formed in ap-type substrate, which includes a first shallow p-type well and asecond shallow n-type well which are formed in mutually differentregions in the first deep n-type well, a third shallow p-type well and afourth shallow n-type well which are formed in mutually differentregions in the second deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the first deep n-type well,and an inverter circuit including an n-channel field effect transistorand a p-channel field effect transistor which are respectively formed inthe third shallow p-type well and the fourth shallow n-type well in thesecond deep n-type well. A fifth shallow p-type well and a sixth shallowp-type well are formed in mutually different regions other thanrespective regions where the first and second deep n-type wells areformed. The semiconductor device further includes a diode including thesixth shallow p-type well and an n-type diffusion layer. A p-typediffusion tap formed in the fifth shallow p-type well is wired to ap-type diffusion tap formed in the third shallow p-type well in thesecond deep n-type well using an interconnection in an n-th layer. Then-type diffusion layer forming the diode is wired to an n-type diffusiontap formed in the second shallow n-type well in the first deep n-typewell using the interconnection in the n-th layer. The respective drainelectrodes of the n-channel field effect transistor and the p-channelfield effect transistor each formed in the first deep n-type well arewired to the respective gate electrodes of the n-channel field effecttransistor and the p-channel field effect transistor each formed in thesecond deep n-type well using an interconnection in an n-th or higherorder layer.

Still another embodiment (seventh method) is a semiconductor devicehaving a first deep n-type well and a second deep n-type well eachformed in a p-type substrate, which includes a first shallow p-type welland a second shallow n-type well which are formed in mutually differentregions in the first deep n-type well, a third shallow p-type well and afourth shallow n-type well which are formed in mutually differentregions in the second deep n-type well, an inverter circuit including ann-channel field effect transistor and a p-channel field effecttransistor which are respectively formed in the first shallow p-typewell and the second shallow n-type well in the first deep n-type well,and an inverter circuit including an n-channel field effect transistorand a p-channel field effect transistor which are respectively formed inthe third shallow p-type well and the fourth shallow n-type well in thesecond deep n-type well. A first bidirectional diode and a secondbidirectional diode are formed in mutually different regions other thanrespective regions where the first and second deep n-type wells areformed. A cathode of the first bidirectional diode, an anode of thesecond bidirectional diode, and an n-type diffusion tap formed in thefourth shallow n-type well are wired using an interconnection in an n-thlayer. An anode of the first bidirectional diode, a cathode of thesecond bidirectional diode, and an n-type diffusion tap formed in thesecond shallow n-type well are wired using the interconnection in then-th layer. The respective drain electrodes of the n-channel fieldeffect transistor and the p-channel field effect transistor each formedin the first deep n-type well are wired to the respective gateelectrodes of the n-channel field effect transistor and the p-channelfield effect transistor each formed in the second deep n-type well usingan interconnection in an n-th or higher order layer.

The following is a brief description of an effect achievable by theembodiment of the representative aspect of the invention disclosed inthe present application.

In a semiconductor device having a triple well structure, a dielectricbreakdown in the gate insulating film of a field effect transistorformed in a triple well region is prevented to allow improvements inmanufacturing yield and product reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a structural view of a semiconductor device used by thepresent inventors for analysis;

FIG. 2( a) is a circuit diagram showing a first circuit in which adielectric breakdown occurs in the gate insulating film of a MIS in acircuit portion forming the semiconductor device of FIG. 1, and FIG. 2(b) is a principal-portion cross-sectional view of circuit elements forillustrating a dielectric breakdown model;

FIG. 3( a) is a circuit diagram showing a second circuit in which adielectric breakdown occurs in the gate insulating film of a MIS in acircuit portion forming the semiconductor device of FIG. 1, and FIG. 3(b) is a principal-portion cross-sectional view of circuit elements forillustrating a dielectric breakdown model;

FIG. 4( a) is a circuit diagram showing a third circuit in which adielectric breakdown occurs in the gate insulating film of a MIS in acircuit portion forming the semiconductor device of FIG. 1, and FIG. 4(b) is a principal-portion cross-sectional view of circuit elements forillustrating a dielectric breakdown model;

FIG. 5 is a circuit diagram illustrating a first example of a firstmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to a first embodiment;

FIG. 6 is a principal-portion cross-sectional view of a first circuitillustrating the first example of the first method shown in FIG. 5mentioned above;

FIG. 7 is a principal-portion plan view of the first circuitillustrating the first example of the first method shown in FIG. 5mentioned above;

FIG. 8 is a circuit diagram illustrating a second example of the firstmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to the first embodiment;

FIG. 9 is a principal-portion cross-sectional view of the first circuitillustrating the second example of the first method shown in FIG. 8mentioned above;

FIG. 10 is a principal-portion plan view of the first circuitillustrating the second example of the first method shown in FIG. 8mentioned above;

FIG. 11 is a circuit diagram illustrating a second method for preventinga dielectric breakdown in the gate insulating film of a MIS according toa second embodiment;

FIG. 12 is a principal-portion cross-sectional view of a first circuitillustrating the second method shown in FIG. 11 mentioned above;

FIGS. 13( a) and 13(b) are principal-portion plan views of the firstcircuit illustrating the second method shown in FIG. 11 mentioned above;

FIG. 14 is a circuit diagram illustrating a third method for preventinga dielectric breakdown in the gate insulating film of a MIS according toa third embodiment;

FIG. 15 is a principal-portion cross-sectional view of a third circuitillustrating the third method shown in FIG. 14 mentioned above;

FIG. 16 is a principal-portion plan view of the third circuitillustrating the third method shown in FIG. 14 mentioned above;

FIG. 17 is a circuit diagram illustrating a first example of a fourthmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to a fourth embodiment;

FIG. 18 is a principal-portion cross-sectional view of a third circuitillustrating the first example of the fourth method shown in FIG. 17mentioned above;

FIG. 19 is a principal-portion plan view of the third circuitillustrating the first example of the fourth method shown in FIG. 17mentioned above;

FIG. 20 is a circuit diagram illustrating a second example of the fourthmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to the fourth embodiment;

FIG. 21 is a principal-portion cross-sectional view of the third circuitillustrating the second example of the fourth method shown in FIG. 20mentioned above;

FIG. 22 is a principal-portion plan view of the third circuitillustrating the second example of the fourth method shown in FIG. 20mentioned above;

FIG. 23 is a circuit diagram illustrating a fifth method for preventinga dielectric breakdown in the gate insulating film of a MIS according toa fifth embodiment;

FIG. 24 is a principal-portion cross-sectional view of the third circuitillustrating the fifth method shown in FIG. 23 mentioned above;

FIG. 25 is a principal-portion plan view of the third circuitillustrating the fifth method shown in FIG. 23 mentioned above;

FIG. 26 is a circuit diagram illustrating a first example of a sixthmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to a sixth embodiment;

FIG. 27 is a principal-portion cross-sectional view of a third circuitillustrating the first example of the sixth method shown in FIG. 26mentioned above;

FIG. 28 is a principal-portion plan view of the third circuitillustrating the first example of the sixth method shown in FIG. 26mentioned above;

FIG. 29 is a circuit diagram illustrating a second example of the sixthmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to the sixth embodiment;

FIG. 30 is a principal-portion cross-sectional view of the third circuitillustrating the second example of the sixth method shown in FIG. 29mentioned above;

FIG. 31 is a circuit diagram illustrating a first example of a seventhmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS according to a seventh embodiment;

FIG. 32 is a principal-portion cross-sectional view of a third circuitillustrating the first example of the seventh method shown in FIG. 31mentioned above;

FIG. 33 is a principal-portion plan view of the third circuitillustrating the first example of the seventh method shown in FIG. 31mentioned above;

FIG. 34 is a circuit diagram illustrating a second example of theseventh method for preventing a dielectric breakdown in the gateinsulating film of a MIS according to the seventh embodiment;

FIG. 35 is a principal-portion cross-sectional view of the third circuitillustrating the second example of the seventh method shown in FIG. 34mentioned above; and

FIG. 36 is a principal-portion plan view of the third circuitillustrating the second example of the seventh method shown in FIG. 34mentioned above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

If necessary for the sake of convenience, each of the followingembodiments will be described hereinbelow by dividing it into aplurality of sections or implementations. However, they are by no meansirrelevant to each other unless shown particularly explicitly, and aremutually related to each other such that one of the sections orimplementations is a variation or a detailed or complementarydescription of some or all of the others.

When the number and the like of elements (including the number,numerical value, amount, and range thereof) are referred to in thefollowing embodiments, they are not limited to specific numbers unlessshown particularly explicitly or unless they are obviously limited tospecific numbers in principle. The number and the like of the elementsmay be not less than or not more than specific numbers. It will beeasily appreciated that, in the following embodiments, the componentsthereof (including also elements and steps) are not necessarilyindispensable unless shown particularly explicitly or unless thecomponents are considered to be obviously indispensable in principle.Likewise, if the configurations, positional relationship, and the likeof the components and the like are referred to in the followingembodiments, the configurations and the like are assumed to includethose substantially proximate or similar thereto unless shownparticularly explicitly or unless obviously they are not in principle.The same shall apply to the foregoing numeric value and the range.

In the drawings used in the following embodiments, even plan views maybe hatched for clear illustration of the drawings. In the followingembodiments, a MISFET (Metal Insulator Semiconductor Field EffectTransistor) representing a field effect transistor will be referred toas a MIS for short, a p-channel MISFET will be referred to as a pMIS forshort, and an n-channel MISFET will be referred to as an nMIS for short.In the following embodiments, when a wafer is mentioned, it typicallyindicates a Si (Silicon) monocrystalline wafer, but it is not limitedthereto. It is assumed that the term “wafer” also indicates a SOI(Silicon On Insulator) wafer, an insulating film substrate for formingan integrated circuit thereon, or the like. It is also assumed that theshapes of wafers are not limited to circular or generally circularshapes, and include a square shape, a rectangular shape, and the like.

In the following embodiments, the wording “deep well” and “shallow well”are used to describe wells forming a triple well structure. The wording“deep and shallow” is associated with a depth from the principal surfaceof a substrate in the thickness direction thereof, and wells are to berelatively and generally classified into the two categories of the “deepwell” and the “shallow well”. Accordingly, the depths of a plurality ofthe “deep wells” are not necessarily constant, and may be different fromeach other. Likewise, the depths of a plurality of the “shallow wells”are not necessarily constant, and may be different from each other.However, the plurality of “deep wells” are constantly formed deeper thanthe plurality of “shallow wells”. The “shallow well” is formed in asubstrate or in the “deep well”, and the plurality of “shallow wells”may also be formed in mutually different regions in the substrate wherethe “deep well” is not formed, or in mutually different regions in the“deep well”.

Throughout the drawings for illustrating the following embodiments,components having the same functions will be provided with the samereference numerals in principle, and a repeated description thereof willbe omitted. Hereinbelow, the embodiments of the present invention willbe described in detail with reference to the drawings.

First, for clearer understanding of the semiconductor devices accordingto the embodiments of the present invention, a description will be givenof the cause of a dielectric breakdown in the gate insulating film of aMIS formed in a triple well region, which has been found by the presentinventors.

As a result of a study conducted by the present inventors, it has beenrevealed that, when coupling holes for coupling a lower-layerinterconnection and an upper-layer interconnection are formed in aninsulating film formed between the lower-layer interconnection and theupper-layer interconnection, a dielectric breakdown occurs in the gateinsulating film of a MIS formed in a triple well region. Because thecoupling holes have been formed by a dry etching method using plasmadischarge, it is presumed that the dielectric breakdown has occurred dueto charging resulting from the plasma discharge. It has been furtherrevealed that a deep well forming the triple well region is charged bythe plasma discharge, and the dielectric breakdown has occurred in thegate insulating film of a MIS which intervenes a path extending from thedeep well to a substrate. In particular, when the deep well occupies alarge area of, e.g., 1 mm² or more, the occurrence of the dielectricbreakdown has been frequently observed. The mechanism of the occurrenceof a dielectric breakdown in the gate insulating film of a MIS due tocharging resulting from plasma discharge is described in detail in“Plasma Charging Damage in Advanced VLSI Technology” by C. Cheung, 1998IEDM Short Course and in “Plasma Currents, Voltages and Chargin” by J.McVittle, 1997 2nd International Symposium on Plasma Process-InducedDamage, Tutorial.

Referring to FIGS. 1 to 4, a specific description will be given of theresult of analyzing a dielectric breakdown in the gate insulating filmof a MIS formed in a triple well region, which has been obtained by thepresent inventors. FIG. 1 is a structural view of a semiconductor deviceused by the present inventors for analysis. FIG. 2( a) is a circuitdiagram showing a first circuit in which a dielectric breakdown occursin the gate insulating film of a MIS in a circuit portion forming thesemiconductor device of FIG. 1 and FIG. 2( b) is a principal-portioncross-sectional view of circuit elements for illustrating a dielectricbreakdown model. FIG. 3( a) is a circuit diagram showing a secondcircuit in which a dielectric breakdown occurs in the gate insulatingfilm of a MIS in a circuit portion forming the semiconductor device ofFIG. 1, and FIG. 3( b) is a principal-portion cross-sectional view ofcircuit elements for illustrating a dielectric breakdown model. FIG. 4(a) is a circuit diagram showing a third circuit in which a dielectricbreakdown occurs in the gate insulating film of a MIS in a circuitportion forming the semiconductor device of FIG. 1, and FIG. 4( b) aprincipal-portion cross-sectional view of circuit elements forillustrating a dielectric breakdown model.

As shown in FIG. 1, a semiconductor device 1 has first regions (regionssurrounded by the double solid frame lines in FIG. 1) where a shallown-type well and a shallow p-type well are formed in mutually differentregions in a substrate, and respective circuit elements are formed inthe shallow n-type well and the shallow p-type well, and second regions(regions surrounded by the dotted frame lines in FIG. 1) where a deepn-type well is formed in a substrate, a shallow n-type well and ashallow p-type well are respectively formed in mutually differentregions in the deep n-type well, and respective circuit elements areformed in the shallow n-type well and the shallow p-type well.

Examples of the first regions mentioned above include an I/O region 2and a control logic region 3. Examples of the second regions mentionedabove include an analog 1 region 4, a phase synchronization circuitregion 5, an analog 2 region 6, an analog 2 control region 7, and a mainlogic region 8. In the main logic region 8, a CPU (Central ProcessingUnit) 9, a DSP (Digital Signal Processor) 10, a RAM (Random AccessMemory) 11, or the like are mounted by way of example. In the peripheralregion of the semiconductor device 1, a plurality of bonding pads BP areformed.

The circuit elements mentioned above are, e.g., MIS transistors, and anexample of signal transfer between individual MIS transistors is shownby the bidirectional arrow in the drawing. Signal transfer is performednot only between individual MIS transistors formed in the first regionsor between individual MIS transistors formed in the second region, butalso between a MIS transistor formed in the first region and a MIStransistor formed in the second transistor or between a MIS transistorformed in the second region and a MIS transistor formed in anothersecond region different from the second region mentioned above.

The present inventors have manufactured the above-mentionedsemiconductor device 1 having the triple well structure, performed afunctional test thereon, and recognized a dielectric breakdown in thegate insulating film of a MIS in a specified circuit. For example, thedielectric breakdown in the gate insulating film of a MIS has beenrecognized in each of the first circuit (1) in which the output stage ofan inverter circuit formed in the first region is wired to the commongate electrode of an inverter circuit formed in the second region, asecond circuit (2) in which the common gate electrode of the invertercircuit formed in the first region is wired to the output stage of theinverter circuit formed in the second region, and the third circuit (3)in which the output stage of the inverter circuit formed in the secondregion is coupled to the common gate electrode of an inverter circuitformed in another second region different from the second regionmentioned above. An inverter circuit is a circuit including a pair of apMIS and an nMIS in which the respective gate electrodes of the pair ofa pMIS and an nMIS are coupled, the respective drain electrodes thereofare coupled, the source electrode of the pMIS is coupled to an n-typewell formed with the pMIS transistor, and the source electrode of thenMIS is coupled to a p-type well formed with the nMIS.

Hereinbelow, a description will be given of a dielectric breakdown modelin the gate insulating film of a MIS transistor in each of the foregoingfirst, second, and third circuits in which the dielectric breakdown hasbeen recognized in the gate insulating film of the MIS transistor.

(1) As shown in FIG. 2( a), the first circuit in which the output stageof the inverter circuit formed in the first region is wired to thecommon gate electrode of the inverter formed in the second regionincludes an inverter circuit INV formed in a substrate Sub, and aninverter circuit INV0 formed in a deep n-type well DNW0.

In the p-type substrate Sub, a shallow n-type well NW and a shallowp-type well PW are formed, while in the shallow n-type well NW, a pMIS100 p is further formed. In the shallow p-type well PW, an nMIS 100 n isfurther formed. The pMIS 100 p and the nMIS 100 n form the invertercircuit INV. In the deep n-type well DNW0, a shallow n-type well NW0 anda shallow p-type well PW0 are formed. In the shallow n-type well NW0, apMIS 200 p is further formed, while in the shallow p-type well PW0, annMIS 200 n is further formed. The pMIS 200 p and the nMIS 200 n form theinverter circuit INV0.

The respective gate electrodes of the pMIS 200 p and the nMIS 200 nwhich form the inverter circuit INV0 are electrically coupled to therespective drain electrodes of the pMIS 100 p and the nMIS 100 n whichform the inverter circuit INV. As a result of the functional testconducted by the present inventors, it has been recognized that adielectric breakdown has occurred in the gate insulating film of thepMIS 200 p or the nMIS 200 n forming the inverter circuit INV0.

Referring to FIG. 2( b), a description will be given of the mechanism ofthe occurrence of a dielectric breakdown in the gate insulating film ofthe pMIS 200 p or the nMIS 200 n forming the inverter circuit INV0.

For example, when positive charge flows into the shallow n-type well NW0in the deep n-type well DNW0 during manufacturing thereof due to plasmadischarge associated with a dry etching method which is implemented whencoupling holes are formed in an interlayer insulating film formed overan interconnection, the positive charge that has flown into the shallown-type well NW0 is accumulated in the deep n-type well DNW0 and in theshallow n-type well NW0 because the deep n-type well DNW0 is notelectrically coupled to the substrate Sub.

On the other hand, since the gate electrode of the nMIS 100 n formed inthe shallow p-type well PW in the substrate Sub is in a floating state,the nMIS 100 n is brought into a conducting state so that a path isformed which extends from the substrate Sub to the gate electrode of thepMIS 200 p formed in the shallow n-type well NW0 in the deep n-type wellDNW0 via the shallow p-type well PW, a p-type diffusion tap PD, the nMIS100 n (the source electrode Sn thereof, the channel region thereof, andthe drain electrode Dn thereof), and the interconnection. As a result,the potential of the gate electrode of the pMIS 200 o formed in theshallow n-type well NW0 in the deep n-type well DNW0 becomes equal tothe potential (0 V) of the substrate Sub. Therefore, it is presumed thatthe voltage applied to the gate insulating film of the pMIS 200 pincreases to cause a dielectric breakdown (the path I indicated by thedotted line in FIG. 2( b)).

For example, when negative charge flows into the shallow p-type well PW0in the deep n-type well DNW0 during manufacturing thereof due to plasmadischarge associated with a dry etching method which is implemented whencoupling holes are formed in the interlayer insulating film formed overthe interconnection, the negative charge that has flown into the shallowp-type well PW0 is accumulated therein because the shallow p-type wellPW0 is formed in the deep n-type well DNW0, and the deep n-type wellDNW0 is not electrically coupled to the substrate Sub.

By contrast, even when negative charge flows into the shallow p-typewell PW in the substrate Sub, the negative charge that has flown intothe shallow p-type well PW is discharged to the substrate Sub since theshallow p-type well PW has the same conductivity type as that of thesubstrate Sub. As a result, the potential of the gate electrode of thenMIS 200 n formed in the shallow p-type well PW0 in the deep n-type wellDNW0 becomes equal to the potential (0 V) of the substrate Sub.Therefore, it is presumed that the voltage applied to the gateinsulating film of the nMIS 200 n increases to cause a dielectricbreakdown (the path II indicated by the dotted line in FIG. 2( b)).

(2) As shown in FIG. 3( a), the second circuit in which the common gateelectrode of the inverter circuit formed in the first region is wired tothe output stage of the inverter circuit formed in the second regionincludes the inverter circuit INV formed in the substrate Sub, and theinverter circuit INV0 formed in the deep n-type well DNW0.

In the p-type substrate Sub, the shallow n-type well NW and the shallowp-type well PW are formed. In the shallow n-type well NW, the pMIS 100 pis further formed, while in the shallow p-type well PW, the nMIS 100 nis further formed. The pMIS 100 p and the nMIS 100 n form the invertercircuit INV. In the deep n-type well DNW0, the shallow n-type well NW0and the shallow p-type well PW0 are formed. In the shallow n-type wellNW0, the pMIS 200 p is further formed. In the shallow p-type well PW0,the nMIS 200 n is further formed. The pMIS 200 p and the nMIS 200 n formthe inverter circuit INV0.

The respective gate electrodes of the pMIS 100 p and the nMIS 100 nwhich form the inverter circuit INV are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. As a result of the functional testconducted by the present inventors, it has been recognized that adielectric breakdown has occurred in the gate insulating film of thepMIS 100 p or the nMIS 100 n forming the inverter circuit INV.

Referring to FIG. 3( b), a description will be given of the mechanism ofthe occurrence of a dielectric breakdown in the gate insulating film ofthe pMIS 100 p or the nMIS 100 n forming the inverter circuit INV.

For example, when positive charge flows into the shallow n-type well NW0in the deep n-type well DNW0 during manufacturing thereof due to plasmadischarge associated with a dry etching method which is implemented whena coupling hole is formed in the interlayer insulating film formed overthe interconnection, the positive charge that has flown into the shallown-type well NW0 is accumulated in the deep n-type well DNW0 and in theshallow n-type well NW0 because the deep n-type well DNW0 is notelectrically coupled to the substrate Sub. Since the gate electrode ofthe pMIS 200 p formed in the shallow n-type well NW0 in the deep n-typewell DNW0 is in a floating state, the pMIS 200 p is brought into aconducting state so that a path is formed which extends from the deepn-type well DNW0 to the gate electrode of the nMIS 100 n formed in theshallow p-type well PW in the substrate Sub via the shallow n-type wellNW0, an n-type diffusion tap ND0, the pMIS 200 p (the source electrodeSp thereof, the channel region thereof, and the drain electrode Dpthereof), and the interconnection.

On the other hand, since the shallow p-type well PW in the substrate Subhas the same conductivity type as that of the substrate Sub, thepotential of the shallow p-type well PW becomes equal to the potential(0 V) of the substrate Sub. Therefore, it is presumed that the voltageapplied to the gate insulating film of the nMIS 100 n formed in theshallow p-type well PW in the substrate Sub increases to cause adielectric breakdown (the path III indicated by the dotted line in FIG.3( b)).

For example, when negative charge flows into the shallow p-type well PW0formed in the deep n-type well DNW0 during manufacturing thereof due toplasma discharge associated with a dry etching method which isimplemented when coupling holes are formed in the interlayer insulatingfilm formed over an interconnection, the negative charge that has flowninto the shallow p-type well PW0 is accumulated therein because theshallow p-type well PW0 is formed in the deep n-type well DNW0, and thedeep n-type well DNW0 is not electrically coupled to the substrate Sub.

By contrast, even when negative charge flows into the shallow p-typewell PW in the substrate Sub, the negative charge that has flown intothe shallow p-type well PW0 is discharged to the substrate Sub since theshallow p-type well PW has the same conductivity type as that of thesubstrate Sub. It is to be noted that, when the inverter circuits eachincluding the pMIS and the nMIS which are respectively formed in theshallow n-type well and the shallow p-type well in the substrate includeone in which the respective gate electrodes of the pMIS and the nMIS arewired to each other and in a floating state, a low-resistance conductingstate is established between the foregoing shallow n-type well and theforegoing shallow p-type well which are formed in mutually differentregions, though the description thereof using the drawings is omittedherein. Accordingly, when such an inverter circuit is present in thesubstrate Sub shown in FIGS. 3( a) and 3(b), the low-resistanceconducting state is established between the shallow n-type well NW andthe shallow p-type well PW each formed in the substrate Sub so that therespective potentials of the shallow n-type well NW and the shallowp-type well PW each formed in the substrate Sub become equal to thepotential (0 V) of the substrate Sub. As a result, it is presumed thatthe voltage applied to each of the gate insulating films of the pMIS 100p and the nMIS 100 p which are respectively formed in the shallow n-typewell NW and the shallow p-type well PW in the substrate Sub increases tocause a dielectric breakdown (the line IV indicated by the dotted linein FIG. 3( b)).

(3) As shown in FIG. 4( a), the third circuit in which the output stageof the inverter circuit formed in the second region is wired to thecommon gate electrode of the inverter formed in another second regiondifferent from the second region mentioned above includes the invertercircuit INV0 formed in the deep n-type well DNW0, and an invertercircuit INV1 formed in a deep n-type well DNW1.

In the deep n-type well DNW0, the shallow n-type well NW0 and theshallow p-type well PW0 are formed. In the shallow n-type well NW0, thepMIS 200 p is further formed, while in the shallow p-type well PW0, thenMIS 200 n is further formed. The area occupied by the deep n-type wellDNW0 is relatively small, and less than, e.g., 1 mm². The pMIS 200 p andthe nMIS 200 n form the inverter circuit INV0. In the deep n-type wellDNW1, a shallow n-type well NW1 and a shallow p-type well PW1 areformed. In the shallow n-type well NW1, a pMIS 300 p is further formed,while in the shallow p-type well PW1, an nMIS 300 n is further formed.The area occupied by the deep n-type well DNW1 is relatively large, andis not less than, e.g., 1 mm². The pMIS 300 p and the nMIS 300 n formthe inverter circuit INV1.

The respective drain electrodes of the pMIS 200 p and the nMIS 200 nwhich form the inverter circuit INV0 are electrically coupled to therespective gate electrodes of the pMIS 300 p and the nMIS 300 n whichform the inverter circuit INV1. As a result of the functional testconducted by the present inventors, it has been recognized that adielectric breakdown has occurred in the gate insulating film of thepMIS 300 p or the nMIS 300 n forming the inverter circuit INV1. Adielectric breakdown is likely to occur in the gate insulating film ofeach of the pMIS 300 p and the nMIS 300 n which are respectively formedin the shallow n-type well NW1 and the shallow p-type well PW1 in thedeep n-type well DNW1 which occupies an area of not less than 1 mm².

Referring to FIG. 4( b), a description will be given of the mechanism ofthe occurrence of a dielectric breakdown in the gate insulating film ofthe pMIS 300 p or the nMIS 300 n forming the inverter circuit INV1.

For example, when positive charge flows into the shallow n-type well NW1in the deep n-type well DNW1 during manufacturing thereof due to plasmadischarge associated with a dry etching method which is implemented whencoupling holes are formed in the interlayer insulating film formed overthe interconnection, the positive charge that has flown into the shallown-type well NW1 is accumulated in the deep n-type well DNW1 and in theshallow n-type well NW1 because the deep n-type well DNW1 is notelectrically coupled to the substrate Sub.

By contrast, when positive charge flows into the shallow n-type well NW0in the deep n-type well DNW0, the positive charge that has flown in theshallow n-type well NW0 is accumulated in the deep n-type well DNW0 andin the shallow n-type well NW0 because the deep n-type well DNW0 is notelectrically coupled to the substrate Sub. However, since the areaoccupied by the deep n-type well DNW0 is smaller than the area occupiedby the deep n-type well DNW1, the amount of charge accumulated in thedeep n-type well DNW0 is smaller than the amount of charge accumulatedin the deep n-type well DNW1. Accordingly, the amount of charge chargingthe gate electrode of the pMIS 300 p in order to couple the drainelectrode of the pMIS 200 p formed in the shallow n-type well NW0 in thedeep n-type well DNW0 to the gate electrode of the pMIS 300 p formed inthe shallow n-type well NW1 in the deep n-type well DNW1 is differentfrom the amount of charge charging the shallow n-type well NW1 in thedeep n-type well DNW1. Therefore, it is presumed that the voltageapplied to the gate insulating film of the pMIS 300 p formed in theshallow n-type well NW1 increases to cause a dielectric breakdown (thepath V indicated by the dotted line in FIG. 4( b)).

For example, when negative charge flows into the shallow p-type well PW1in the deep n-type well DNW1 during manufacturing thereof due to plasmadischarge associated with a dry etching method which is implemented whencoupling holes are formed in the interlayer insulating film formed overthe interconnection, the negative charge that has flown in the shallowp-type well PW1 is accumulated therein because the shallow p-type wellPW1 is formed in the deep n-type well DNW1, and the deep n-type wellDNW1 is not electrically coupled to the substrate Sub. On the otherhand, negative charge that has flown in the shallow p-type well PW0 inthe deep n-type well DNW0 is likewise accumulated in the shallow p-typewell PW0 in the deep n-type well DNW0. However, the area occupied by thep-type well PW0 is smaller than the area occupied by the p-type well PW1so that the amount of charge accumulated in the p-type well PW1 islarger than the amount of charge accumulated in the p-type well PW0. Forexample, because the gate electrode of the pMIS 200 p formed in theshallow n-type well NW0 in the deep n-type well DNW0 is in a floatingstate, the pMIS 200 p is brought into a conducting state so that a pathis formed which extends from the deep n-type well DNW0 to the gateelectrode of the nMIS 300 n formed in the shallow p-type well PW1 in thedeep n-type well DNW1 via the shallow n-type well NW0, the n-typediffusion tap ND0, the pMIS 200 n (the source electrode Sp thereof, thechannel region thereof, and the drain electrode Dp thereof), and theinterconnection. As a result, it is presumed that the voltage applied tothe gate insulating film of the nMIS 300 n formed in the shallow p-typewell PW1 in the deep n-type well DNW1 increases to cause a dielectricbreakdown (the path VI indicated by the dotted line in FIG. 4( b)).

The present inventors have verified that a dielectric breakdown occursin the gate insulating film of a MIS not only in the first, second, andthird circuits described above, but also in a fourth circuit in which,e.g., the common gate electrode of an inverter circuit formed in a deepn-type well is wired to the drain electrode of a MIS formed in thesubstrate and in a fifth circuit in which the output stage of aninverter circuit formed in a deep n-type well is wired to the gateelectrode of a MIS formed in the deep n-type well. In each of the fourthand fifth circuits, a dielectric breakdown in the gate insulating filmof a MIS can be prevented by, e.g., disposing an inverter circuit whichdoes not contribute to a circuit operation in the deep n-type well,wiring a shallow p-type well to the substrate using a lowermost-layerinterconnection, wiring the common gate electrode to a shallow n-typewell using an uppermost-layer interconnection, and discharging chargeaccumulated in the deep n-type well. As for a method for preventing adielectric breakdown in the gate insulating film of a MIS in the fourthand fifth circuits, it is disclosed in Japanese Patent Application No.2008-6436 (filed by Hiraiwa, et al. on Jan. 16, 2008).

According to the result of the analysis described heretofore, inpreventing a dielectric breakdown in the gate insulating film of a MIS,it is effective to reduce the voltage applied to the gate insulatingfilm of the MIS to a value of not more than the dielectric breakdownvoltage of the gate insulating film of the MIS, or eliminate thepotential difference between deep wells formed in mutually differentregions. Hereinbelow, a detailed description will be given of the methodfor preventing a dielectric breakdown in the gate insulating film of aMIS in the embodiments of the present invention.

Embodiment 1

In the present first embodiment, a description will be given of twoexamples (first and second examples) of a first method for preventing adielectric breakdown in the gate insulating film of a MIS in each of theforegoing first circuit (FIGS. 2( a) and 2(b) mentioned above) and theforegoing second circuit (FIGS. 3( a) and 3(b) mentioned above). First,the first example of the first method will be described with referenceto FIGS. 5 to 7, and then the second example of the first method will bedescribed with reference to FIGS. 8 to 10. FIG. 5 is a circuit diagramillustrating the first example of the first method for preventing adielectric breakdown in the gate insulating film of a MIS according tothe present first embodiment. FIG. 6 is a principal-portioncross-sectional view of the first circuit illustrating the first exampleof the first method shown in FIG. 5 mentioned above. FIG. 7 is aprincipal-portion plan view of the first circuit illustrating the firstexample of the first method shown in FIG. 5 mentioned above. FIG. 8 is acircuit diagram illustrating the second example of the first method forpreventing a dielectric breakdown in the gate insulating film of a MISaccording to the present first embodiment. FIG. 9 is a principal-portioncross-sectional view of the first circuit illustrating the secondexample of the first method shown in FIG. 8 mentioned above. FIG. 10 isa principal-portion plan view of the first circuit illustrating thesecond example of the first method shown in FIG. 8 mentioned above.

First, the first example of the first method will be described.

As described above, the first circuit (FIGS. 2( a) and 2(b) mentionedabove) includes the inverter circuit INV formed in the substrate Sub,and the inverter circuit INV0 formed in the deep n-type well DNW0. Therespective gate electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0 are electrically coupled to therespective drain electrodes of the pMIS 100 p and the nMIS 100 n whichform the inverter circuit INV. In the gate insulating film of the pMIS200 p or the nMIS 200 n forming the inverter circuit INV0, a dielectricbreakdown has occurred.

On the other hand, as described above, the second circuit (FIGS. 3( a)and 3(b) mentioned above) includes the inverter circuit INV formed inthe substrate Sub, and the inverter circuit INV0 formed in the deepn-type well DNW0. The respective gate electrodes of the pMIS 100 p andthe nMIS 100 n which form the inverter circuit INV are electricallycoupled to the respective drain electrodes of the pMIS 200 p and thenMIS 200 n which form the inverter circuit INV0. In the gate insulatingfilm of the pMIS 100 p or the nMIS 100 n forming the inverter circuitINV, a dielectric breakdown has occurred.

As shown in FIG. 5, in the first example of the first method accordingto the present first embodiment, a shallow p-type well PW100 is formedin the substrate Sub, and a p-type diffusion tap PD100 for potentialfixation is formed in the shallow p-type well PW100. The p-typediffusion tap PD100 is coupled to a p-type diffusion tap PD0 forpotential fixation which is formed in the shallow p-type well PW0 in thedeep n-type well DNW0 using an interconnection in a second or higherorder layer.

The wiring of the inverter circuit INV formed in the substrate Sub tothe inverter circuit INV0 formed in the deep n-type well DNW0, i.e., thewiring of the respective drain electrodes of the pMIS 100 p and the nMIS100 n which form the inverter circuit INV to the respective gateelectrodes of the pMIS 200 p and the nMIS 200 p which form the invertercircuit INV0, and the wiring of the respective gate electrodes of thepMIS 100 p and the nMIS 100 n which form the inverter circuit INV to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0 are performed using an interconnection inthe same layer as that of the interconnection used to wire the p-typediffusion tap PD100 to the p-type diffusion tap PD0, or aninterconnection in a layer higher in order than that. For example, inthe case where the wiring of the p-type diffusion tap PD100 to thep-type diffusion tap PD0 is performed using an interconnection in asecond layer, the wiring of the inverter circuit INV formed in thesubstrate Sub to the inverter circuit INV0 formed in the deep n-typewell DNW0 is performed using an interconnection in a second or higherorder layer. In the case where the wiring of the p-type diffusion tapPD100 to the p-type diffusion tap PD0 is performed using aninterconnection in a third layer, the wiring of the inverter circuit INVformed in the substrate Sub to the inverter circuit INV0 formed in thedeep n-type well DNW0 is performed using an interconnection in a thirdor higher order layer.

As shown in FIG. 6, in the first circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 100 p andthe nMIS 100 n which form the inverter circuit INV and the respectivegate electrodes of the pMIS 200 p and the nMIS 200 n which form theinverter circuit INV0), a parasitic pn diode is formed by the wiring ofthe p-type diffusion tap PD100 to the p-type diffusion tap PD0. Theparasitic pn diode forms a forward discharge path extending from thesubstrate Sub to the deep n-type well DNW0 via the shallow p-type wellPW100, the p-type diffusion tap PD100, the interconnection, the p-typediffusion tap PD0, and the shallow p-type well PW0.

In the first circuit, in a manufacturing step of forming the couplingholes for coupling the inverter circuit INV0 formed in the deep n-typewell DNW0 to the inverter circuit INV formed in the substrate Sub, thegate electrode of the pMIS 200 p formed in the shallow n-type well NW0in the deep n-type well DNW0 is brought into a floating state to bringthe pMIS 200 p into a conducting state. As a result, a discharge path isformed which extends from the deep n-type well DNW0 to the substrate Subvia the shallow n-type well NW0, the n-type diffusion tap ND0, the pMIS200 p (the source electrode Sp thereof, the channel region thereof, andthe drain region Dp thereof), the shallow p-type well PW0, the p-typediffusion tap PD0, the interconnection, the p-type diffusion tap PD100,and the shallow p-type well PW100.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 200 p and the nMIS 200 n which are respectively formed in theshallow n-type well NW0 and the shallow p-type well PW0 in the deepn-type well DNW0.

In the second circuit (circuit in which the respective gate electrodesof the pMIS 100 p and the nMIS 100 n which form the inverter circuit INVare wired to the respective drain electrodes of the pMIS 200 p and thenMIS 200 n which form the inverter circuit INV0) also, the same effectas obtained in the first circuit described above can be obtained, thoughthe description thereof is omitted herein. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 100 p and the nMIS 100 n which are respectively formed in theshallow n-type well NW and the shallow p-type well PW in the substrateSub.

FIG. 7 shows a principal-portion plan view of the p-type diffusion tapPD100 formed in the substrate Sub and the p-type diffusion tap PD0formed in the shallow p-type well PW0 in the deep n-type well DNW0.

In the shallow p-type well PW100 in the substrate Sub, the p-typediffusion tap PD100 is formed, while in the interlayer insulating film(not shown) formed over the substrate Sub, coupling holes CNT1 areformed to reach the p-type diffusion tap PD100. Likewise, in the shallowp-type well PW0 in the deep n-type well DNW0, the p-type diffusion tapPD0 is formed, while in the interlayer insulating film (not shown)formed over the substrate Sub (deep n-type well DNW0), the couplingholes CNT1 are formed to reach the p-type diffusion tap PD0. There isalso formed an interconnection M1 in a first layer which is electricallycoupled to the p-type diffusion tap PD100 or the p-type diffusion tapPD0 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed coupling holes CNT2 reaching the interconnection M1 in thefirst layer which is electrically coupled to the p-type diffusion tapPD100 formed in the shallow p-type well PW100 in the substrate Sub, andthe coupling holes CNT2 reaching the interconnection M1 in the firstlayer which is electrically coupled to the p-type diffusion tap PD0formed in the shallow p-type well PW0 in the deep n-type well DNW0. Thep-type diffusion tap PD100 formed in the shallow p-type well PW100 inthe substrate Sub is electrically coupled to the p-type diffusion tapPD0 formed in the shallow p-type well PW0 in the deep n-type well DNW0using an interconnection M2 in the second layer.

Next, the second example of the first method will be described.

In the second example of the first method also, a description is givenof the method for preventing a dielectric breakdown in the gateinsulating film of the pMIS 200 p or the nMIS 200 n forming the invertercircuit INV0, which occurs in the first circuit (FIGS. 2( a) and 2(b)mentioned above), and a dielectric breakdown in the gate insulating ofthe pMIS 100 p or the nMIS 100 n forming the inverter circuit INV, whichoccurs in the second circuit (FIGS. 3( a) and 3(b) mentioned above), inthe same manner as in the first example of the first method describedabove. The first and second examples of the first method are differentin that, in the first example, the shallow p-type well PW100 is formedin the substrate Sub, and the p-type diffusion tap PD100 which iselectrically coupled to the p-type diffusion tap PD0 formed in theshallow p-type well PW0 in the deep n-type well DNW0 is formed in theshallow p-type well PW100, while in the second example, the p-typediffusion tap PD for potential fixation which is formed in the shallowp-type well PW in the substrate Sub is used also as a p-type diffusiontap for discharging accumulated charge.

As shown in FIG. 8, in the second example of the first method accordingto the present first embodiment, the p-type diffusion tap PD forpotential fixation is formed in the shallow p-type well PW in thesubstrate Sub where the nMIS 100 n is formed, while the p-type diffusiontap PD0 for potential fixation is formed in the shallow p-type well NW0in the deep n-type well DNW0 where the nMIS 200 n is formed. The p-typediffusion tap PD is further coupled to the p-type diffusion tap PD0using an interconnection in a second or higher order layer.

The wiring of the inverter circuit INV formed in the substrate Sub tothe inverter circuit INV0 formed in the deep n-type well DNW0, i.e., thewiring of the respective drain electrodes of the pMIS 100 p and the nMIS100 n which form the inverter circuit INV to the respective gateelectrodes of the pMIS 200 p and the nMIS 200 n which form the invertercircuit INV0, and the wiring of the respective gate electrodes of thepMIS 100 p and the nMIS 100 n which form the inverter circuit INV to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0 are performed using the interconnectionin the same layer as that of the interconnection used to wire the p-typediffusion tap PD to the p-type diffusion tap PD0, or an interconnectionin a layer higher in order than that. For example, in the case where thewiring of the p-type diffusion tap PD to the p-type diffusion tap PD0 isperformed using the interconnection in the second layer, the wiring ofthe inverter circuit INV formed in the substrate Sub to the invertercircuit INV0 formed in the deep n-type well DNW0 is performed using aninterconnection in a second or higher order layer. In the case where thewiring of the p-type diffusion tap PD to the p-type diffusion tap PD0 isperformed using the interconnection in the third layer, the wiring ofthe inverter circuit INV formed in the substrate Sub to the invertercircuit INV0 formed in the deep n-type well DNW0 is performed using aninterconnection in a third or higher order layer.

As shown in FIG. 9, in the first circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 100 p andthe nMIS 100 n which form the inverter circuit INV and the respectivegate electrodes of the pMIS 200 p and the nMIS 200 n which form theinverter circuit INV0), a parasitic pn diode is formed by the wiring ofthe p-type diffusion tap PD to the p-type diffusion tap PD0. Theparasitic pn diode forms a discharge path extending from the substrateSub to the deep n-type well DNW0 via the shallow p-type well PW, thep-type diffusion tap PD, the interconnection, the p-type diffusion tapPD0, and the shallow p-type well PW0.

In the first circuit, in the manufacturing step of forming the couplingholes for coupling the inverter circuit INV formed in the substrate Subto the inverter circuit INV0 formed in the deep n-type well DNW0, therespective gate electrodes of the pMIS 200 p and the nMIS 200 n whichare respectively formed in the shallow n-type well NW0 and the shallowp-type well PW0 in the deep n-type well DNW0 are each brought into afloating state to bring each of the pMIS 200 p and the nMIS 200 n into aconducting state. As a result, a discharge path is formed which extendsfrom the deep n-type well DNW0 to the substrate Sub via the shallown-type well NW0, the n-type diffusion tap ND0, the pMIS 200 p (thesource electrode Sp thereof, the channel region thereof, and the drainregion Dp thereof), the nMIS 200 n (the drain electrode Dn thereof, thechannel region thereof, and the source electrode Sn thereof), theinterconnection, the p-type diffusion tap PD, and the shallow p-typewell WP.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 200 p and the nMIS 200 n which are respectively formed in theshallow n-type well NW0 and the shallow p-type well PW0 in the deepn-type well DNW0.

It is to be noted that a parasitic diode Di is present between theshallow p-type well PW formed in the substrate Sub and the sourceelectrode Sn of the nMIS 100 n formed in the shallow p-type well PW.However, since the substrate Sub, the shallow p-type well PW, and thep-type diffusion tap DP are all p-type semiconductor regions, it isconsidered that the discharge path extending from the substrate Subthrough the shallow p-type well PW and the p-type diffusion tap DP ismore dominant than the parasitic diode Di.

In the second circuit (circuit in which the respective gate electrodesof the pMIS 100 p and the nMIS 100 n which form the inverter circuit INVare wired to the respective drain electrodes of the pMIS 200 p and thenMIS 200 n which form the inverter circuit INV0) also, the same effectas obtained in the first circuit described above can be obtained, thoughthe description thereof is omitted herein. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 100 p and the nMIS 100 n which are respectively formed in theshallow n-type well NW and the shallow p-type well PW in the substrateSub.

FIG. 10 shows a principal-portion plan view of the inverter circuit INV0formed in the substrate Sub and the inverter circuit INV0 formed in thedeep n-type well DNW0.

In the shallow p-type well PW in the substrate Sub, the nMIS 100 n isformed. The nMIS 100 n includes n-type diffusion layers DIFn forming asource electrode and a drain electrode. On the other hand, in theshallow n-type well NW in the substrate Sub, the pMIS 100 p is formed.The pMIS 100 p includes p-type diffusion layers DIFp forming a sourceelectrode and a drain electrode. In the interlayer insulating film (notshown) over the substrate Sub, the coupling holes CNT1 are formed incontact with the drain electrode (n-type diffusion layer DIFn) of thenMIS 100 n or with the drain electrode (p-type diffusion layer DIFp) ofthe pMIS 100 p. Through the coupling holes CNT1, the respective drainelectrodes of the nMIS 100 n and the pMIS 100 p are electrically coupledvia the interconnection M1 in the first layer.

In the shallow n-type well NW in the substrate Sub, an n-type diffusiontap ND is formed, while in the shallow p-type well PW, the p-typediffusion tap PD is formed. In the interlayer insulating film (notshown) over the substrate Sub, the coupling holes CNT1 are formed incontact with the n-type diffusion tap ND or with the source electrode(p-type diffusion layer DIFp) of the pMIS 100 p. Through the couplingholes CNT1, the n-type diffusion tap ND and the source electrode of thepMIS 100 p are electrically coupled via the interconnection in the firstlayer. The gate electrode of the nMIS 100 n and the gate electrode ofthe pMIS 100 p are formed of a conductive film in the same common layer.Through the coupling holes CNT1 formed in the interlayer insulating film(not shown) formed over the substrate Sub, the interconnection M1 in thefirst layer is electrically coupled to the conductive film.

Likewise, in the shallow p-type well PW0 in the deep n-type well DNW0,the nMIS 200 n is formed. The nMIS 200 n includes the n-type diffusionlayers DIFn forming a source electrode and a drain electrode. On theother hand, in the shallow n-type well NW in the deep n-type well DNW0,the pMIS 200 p is formed. The pMIS 200 p includes the p-type diffusionlayers DIFp forming a source electrode and a drain electrode. In theinterlayer insulating film (not shown) over the substrate Sub (the deepn-type well DNW0), the coupling holes CNT1 are formed in contact withthe drain electrode (n-type diffusion layer DIFn) of the nMIS 200 n orwith the drain electrode (p-type diffusion layer DIFp) of the pMIS 200p. Through the coupling holes CNT1, the respective drain electrodes ofthe nMIS 200 n and the pMIS 200 p are electrically coupling via theinterconnection M1 in the first layer.

In the shallow n-type well NW0 in the deep n-type well DNW0, the n-typediffusion tap ND0 is formed, while in the shallow p-type well PW0, thep-type diffusion tap PD0 is formed. In the interlayer insulating film(not shown) over the substrate Sub (the deep n-type well DNW0), thecoupling holes CNT1 are formed in contact with the n-type diffusion tapND0 or with the source electrode (p-type diffusion layer DIFp) of thepMIS 200 p. Through the coupling holes CNT1, the n-type diffusion tapND0 and the source electrode of the pMIS 200 p are electrically coupledvia the interconnection M1 in the first layer. The gate electrode of thenMIS 200 n and the gate electrode of the pMIS 200 p are formed of aconductive film in the same common layer. Through the coupling holesCNT1 formed in the interlayer insulating film (not shown) formed overthe substrate Sub, the interconnection M1 in the first layer iselectrically coupled to the conductive film.

There are further formed the interconnection M1 in the first layer whichis electrically coupled to the common gate electrode of the pMIS 100 pand the nMIS 100 n each formed in the substrate Sub through the couplingholes CNT1, and the interconnection M1 in the first layer which iselectrically coupled to each of the respective drain electrodes of thepMIS 200 p and the nMIS 200 n each formed in the deep n-type well DNW0through the coupling holes CNT1. Additionally, the coupling holes CNT2are formed in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnections M1 in the first layer.Through the coupling holes CNT2, the interconnection in the first layerwhich is electrically coupled to the common gate electrode of the pMIS100 p and the nMIS 100 p is electrically coupled to the interconnectionM1 in the first layer which is electrically coupled to each of therespective drain electrodes of the pMIS 200 p and the nMIS 200 n via theinterconnection M2 in the second layer.

To the p-type diffusion tap PD formed in the shallow p-type well PW inthe substrate Sub or to the p-type diffusion tap PD0 formed in theshallow p-type well PW0 in the deep n-type well DNW0, theinterconnections M1 in the first layer are electrically coupled throughthe coupling holes CNT1. In the interlayer insulating film (not shown)formed over the substrate Sub to cover the interconnections M1 in thefirst layer, the coupling holes CNT2 are formed. Through the couplingholes CNT2, the p-type diffusion taps PD and PD0 are electricallycoupled via the interconnection M2 in the second layer.

In the present first embodiment, it is assumed that the p-type diffusiontaps PD and PD100 are wired to the p-type diffusion tap PD0 using aninterconnection in a second or higher order layer. This is because,since an interconnection in a first layer is generally used as a signalinterconnection, it is difficult to couple the p-type diffusion taps PDand PD100 to the p-type diffusion tap PD0 using the interconnection inthe first layer. Therefore, in the case where layout using theinterconnection in the first layer is possible, the interconnection inthe first layer can also be used to wire the p-type diffusion taps PDand PD100 to the p-type diffusion tap PD0.

Thus, according to the present first embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0 due to a plasma charge-up phenomenon in,e.g., a dry etching step, the charge can be easily discharged to thesubstrate Sub. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 200 p and thenMIS 200 n which are respectively formed in the shallow n-type well NW0and the shallow n-type well PW0 in the deep n-type well DNW0 to form theinverter circuit INV0, and a dielectric breakdown in each of the gateinsulating films of the pMIS 100 p and the nMIS 100 n which arerespectively formed in the shallow n-type well NW and the shallow p-typewell PW in the substrate Sub to form the inverter circuit INV. Inparticular, when, e.g., the shallow p-type well PW formed in thesubstrate Sub and the shallow p-type well PW0 formed in the deep n-typewell DNW0 are at the same potential, the first method in the presentfirst embodiment serves as an effective means.

Embodiment 2

In the present second embodiment, a description will be given of asecond method for preventing a dielectric breakdown in the gateinsulating film of a MIS in each of the foregoing first circuit (FIGS.2( a) and 2(b) mentioned above) and the foregoing second circuit (FIGS.3( a) and 3(b) mentioned above) with reference to FIGS. 11 to 13. FIG.11 is a circuit diagram illustrating the second method for preventing adielectric breakdown in the gate insulating film of a MIS according tothe present second embodiment. FIG. 12 is a principal-portioncross-sectional view of the first circuit illustrating the second methodshown in FIG. 11 mentioned above. FIGS. 13( a) and 13(b) areprincipal-portion plan views of the first circuit illustrating thesecond method shown in FIG. 11 mentioned above.

As described above, the first circuit (FIGS. 2( a) and 2(b) mentionedabove) includes the inverter circuit INV formed in the substrate Sub,and the inverter circuit INV0 formed in the deep n-type well DNW0. Therespective gate electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0 are electrically coupled to therespective drain electrodes of the pMIS 100 p and the nMIS 100 n whichform the inverter circuit INV. In the gate insulating film of the pMIS200 p or the nMIS 200 n which form the inverter circuit INV0, adielectric breakdown has occurred.

On the other hand, as described above, the second circuit (FIGS. 3( a)and 3(b) mentioned above) includes the inverter circuit INV formed inthe substrate Sub, and the inverter circuit INV0 formed in the deepn-type well DNW0. The respective gate electrodes of the pMIS 100 p andthe nMIS 100 n which form the inverter circuit INV are electricallycoupled to the respective drain electrodes of the pMIS 200 p and thenMIS 200 n which form the inverter circuit INV0. In the gate insulatingfilm of the pMIS 100 p or the nMIS 100 n forming the inverter circuitINV, a dielectric breakdown has occurred.

As shown in FIG. 11, in the second method according to the presentsecond embodiment, a shallow p-type well PW200 in the substrate Sub andan n-type diffusion layer in the shallow p-type well PW200 form a pndiode Di200. The cathode of the pn diode Di200 and the n-type diffusiontap ND0 for potential fixation which is formed in the shallow n-typewell NW0 in the deep n-type well DNW0 are coupled using aninterconnection in a second or higher order layer.

The wiring of the inverter circuit INV formed in the substrate Sub tothe inverter circuit INV0 formed in the deep n-type well DNW0, i.e., thewiring of the respective drain electrodes of the pMIS 100 p and the nMIS100 n which form the inverter circuit INV to the respective gateelectrodes of the pMIS 200 p and the nMIS 200 which form the invertercircuit INV0, and the wiring of the respective gate electrodes of thepMIS 100 p and the nMIS 100 n which form the inverter circuit INV to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0 are performed using an interconnection inthe same layer as that of the interconnection used to wire the n-typediffusion layer of the pn diode Di200 to the n-type diffusion tap ND0,or an interconnection in a layer higher in order than that. For example,in the case where the wiring of the n-type diffusion layer of the pndiode Di200 to the n-type diffusion tap ND0 is performed using theinterconnection in the second layer, the wiring of the inverter circuitINV formed in the substrate Sub to the inverter circuit INV0 formed inthe deep n-type well DNW0 is performed using an interconnection in asecond or higher order layer. In the case where the wiring of the n-typediffusion layer of the pn diode Di200 to the n-type diffusion tap ND0 isperformed using the interconnection in the third layer, the wiring ofthe inverter circuit INV formed in the substrate Sub to the invertercircuit INV0 formed in the deep n-type well DNW0 is performed using aninterconnection in a third or higher order layer.

As shown in FIG. 12, in the first circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 100 p andthe nMIS 100 n which form the inverter circuit INV and the respectivegate electrodes of the pMIS 200 p and the nMIS 200 n which form theinverter circuit INV0), when the potential of the substrate Sub ishigher than the potential of the deep n-type well DNW0, the pn diodeDi200 forms a forward discharge path extending from the substrate Sub tothe deep n-type well DNW0 via the shallow p-type well PW200, an n-typediffusion layer DIn, the interconnection, the n-type diffusion tap ND0,and the shallow n-type well NW0. When the potential of the substrate Subis lower than the potential of the deep n-type well DNW0, the pn diodeDi200 is in a reverse direction. For example, in a manufacturing stepusing plasma discharge such as a dry etching step, optical excitationdue to light emission or thermal excitation due to heat increases aleakage current in the reverse direction to form a discharge path.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 200 p and the nMIS 200 n which are respectively formed in theshallow n-type well NW0 and the shallow p-type well PW0 in the deepn-type well DNW0.

In the second circuit (circuit in which the respective gate electrodesof the pMIS 100 p and the names 100 n which form the inverter circuitINV are wired to the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0) also, the sameeffect as obtained in the first circuit described above can be obtained,though the description thereof is omitted herein. Therefore, it ispossible to prevent a dielectric breakdown in each of the gateinsulating films of the pMIS 100 p and the nMIS 100 n which arerespectively formed in the shallow n-type well NW and the shallow p-typewell PW in the substrate Sub.

FIGS. 13( a) and 13(b) show principal-portion plan views of the pn diodeDi200 formed in the substrate Sub and the n-type diffusion tap ND0formed in the deep n-type well DNW0. FIG. 13( a) is a principal-portionplan view of the pn diode Di200 formed of the n-type diffusion layer DInwhich is formed in the shallow p-type well PW200 in the substrate Sub.FIG. 13( b) is a principal-portion plan view of the pn diode Di200formed of the n-type diffusion layer DIn which is formed in the shallowp-type well PW200 in the substrate Sub, and surrounded by a guard ringformed of a p-type diffusion layer DIp.

As shown in FIG. 13( a), the n-type diffusion layer DIn is formed in theshallow p-type well PW200 in the substrate Sub. In the interlayerinsulating film (not shown) formed over the substrate Sub, the couplingholes CNT1 are formed to reach the n-type diffusion layer DIn. Likewise,in the shallow n-type well NW0 in the deep n-type well DNW0, the n-typediffusion tap ND0 is formed. In the interlayer insulating film (notshown) formed over the substrate Sub (the deep n-type well DNW0), thecoupling holes CNT1 are formed to reach the n-type diffusion tap ND0.There is also formed the interconnection M1 in the first layer which iselectrically coupled to the n-type diffusion layer DIn or the n-typediffusion tap ND0 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusionlayer DIn formed in the shallow p-type well PW200 in the substrate Sub,and the coupling holes CNT2 reaching the interconnection M1 in the firstlayer which is electrically coupled to the n-type diffusion tap ND0formed in the shallow n-type well NW0 in the deep n-type well DNW0. Then-type diffusion layer DIn formed in the shallow p-type well PW200 inthe substrate Sub is electrically coupled to the n-type diffusion tapND0 formed in the shallow n-type well NW0 in the deep n-type well DNW0using the interconnection M2 in the second layer.

As shown in FIG. 13( b), the n-type diffusion layer DIn is formed in theshallow p-type well PW200 which is formed in the substrate Sub, and thep-type diffusion layer DIp is further formed to surround the n-typediffusion layer DIn at a given distance therefrom. In the interlayerinsulating film (not shown) formed over the substrate Sub, the couplingholes CNT1 are formed to reach the n-type diffusion layer DIn or thep-type diffusion layer DIp. In the shallow n-type well NW0 in the deepn-type well DNW0, the n-type diffusion tap ND0 is formed. In theinterlayer insulating film (not shown) formed over the substrate Sub(the deep n-type well DNW0), the coupling holes CNT1 are formed to reachthe n-type diffusion tap ND0. There is also formed the interconnectionM1 in the first layer which is electrically coupled to the n-typediffusion layer DIn, the p-type diffusion layer DIp, or the n-typediffusion tap ND0 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusionlayer DIn formed in the shallow p-type well PW200 in the substrate Sub,and the coupling holes CNT2 reaching the interconnection M1 in the firstlayer which is electrically coupled to the n-type diffusion tap ND0formed in the shallow n-type well NW0 in the deep n-type well DNW0. Then-type diffusion layer DIn formed in the shallow p-type well PW200 inthe substrate Sub is electrically coupled the n-type diffusion tap ND0formed in the shallow n-type well NW0 in the deep n-type well DNW0 usingthe interconnection M2 in the second layer.

In the present second embodiment, it is assumed that the n-typediffusion tap ND0 is wired to the cathode of the pn diode Di200 using aninterconnection in a second or higher order layer. However, in the casewhere layout using the interconnection in the first layer is possible,the interconnection in the first layer can also be used to wire then-type diffusion tap ND0 to the cathode of the pn diode Di200.

Thus, according to the present second embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0, the charge can be easily discharged tothe substrate Sub, in the same manner as in the first embodimentdescribed above. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 200 p and thenMIS 200 n which are respectively formed in the shallow n-type well NW0and the shallow p-type well PW0 in the deep n-type well DNW0 to form theinverter circuit INV0, and a dielectric breakdown in each of the gateinsulating films of the pMIS 100 p and the nMIS 100 n which arerespectively formed in the shallow n-type well NW and the shallow p-typewell PW in the substrate Sub to form the inverter circuit INV. Inparticular, in the case where the nMIS 100 n and the pMIS 100 p whichare respectively formed in the shallow p-type well PW and the shallown-type well NW in the substrate Sub are formed into a digital circuit,the nMIS 200 n and the pMIS 200 p which are respectively formed in theshallow p-type well PW0 and the shallow n-type well NW0 in the deepn-type well DNW0 are formed into an analog circuit, and each of the nMIS100 n, the pMIS 100 p, the pMIS 200 p, and the nMIS 200 n has adedicated power supply or ground, i.e., in the case where the powersupply of the shallow n-type well NW formed in the substrate Sub isdifferent from the power supply of the shallow n-type well NW0 formed inthe deep n-type well DNW0, and the power supply of the shallow p-typewell PW formed in the substrate Sub is different from the power supplyof the shallow p-type well PW0 formed in the deep n-type well DNW0, thesecond method in the present second embodiment serves as an effectivemeans.

Embodiment 3

In the present third embodiment, a description will be given of a thirdmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS in the foregoing third circuit (FIGS. 4( a) and 4(b) mentionedabove) with reference to FIGS. 14 to 16. FIG. 14 is a circuit diagramillustrating the third method for preventing a dielectric breakdown inthe gate insulating film of a MIS according to the present thirdembodiment. FIG. 15 is a principal-portion cross-sectional view of thethird circuit illustrating the third method shown in FIG. 14 mentionedabove. FIG. 16 is a principal-portion plan view of the third circuitillustrating the third method shown in FIG. 14 mentioned above.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 14, in the third method according to the present thirdembodiment, the n-type diffusion tap ND0 for potential fixation isformed in the shallow n-type well NW0 in the deep n-type well DNW0 wherethe pMIS 200 p is formed, while an n-type diffusion tap ND1 forpotential fixation is formed in the shallow n-type well NW1 in the deepn-type well DNW1. The n-type diffusion tap ND0 is further coupled to then-type diffusion tap ND1 using an interconnection in a second or higherorder layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to wire the n-typediffusion tap ND0 to the n-type diffusion tap ND1, or an interconnectionin a layer higher in order than that. For example, in the case where thewiring of the n-type diffusion tap ND0 to the n-type diffusion tap ND1is performed using the interconnection in the second layer, the wiringof the inverter circuit INV0 formed in the deep n-type diffusion wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a second or higher order layer. Inthe case where the wiring of the n-type diffusion tap ND0 to the n-typediffusion tap ND1 is performed using the interconnection in the thirdlayer, the wiring of the inverter circuit INV0 formed in the deep n-typewell DNW0 to the inverter circuit INV1 formed in the deep n-type wellDNW1 is performed using an interconnection in a third or higher orderlayer.

As shown in FIG. 15, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), the wiring of the n-type diffusion tap ND0 tothe n-type diffusion tap ND1 forms a discharge path (or a discharge pathin a direction reverse to that of the discharge path) extending from thedeep n-type well DNW1 to the deep n-type well DNW0 via the shallown-type well NW1, the n-type diffusion tap ND1, the interconnection, then-type diffusion tap ND0, and the shallow n-type well NW0. As a result,the deep n-type well DNW0 and the deep n-type well DNW1 which are formedin mutually different regions are at the same potential.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW1, the shallow n-typewell NW1, and the shallow p-type well PW1 in a manufacturing step usingplasma discharge such as, e.g., a dry etching step to another wellregion such as, e.g., the deep n-type well DNW0. As a result, thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0 is reduced. Therefore, it is possible to prevent adielectric breakdown in each of the gate insulating films of the pMIS300 p and the nMIS 300 n which are respectively formed in the shallown-type well NW1 and the shallow p-type well PW1 in the deep n-type wellDNW1.

FIG. 16 shows a principal-portion plan view of the n-type diffusion tapND0 formed in the deep n-type well DNW0 and the n-type diffusion tap ND1formed in the deep n-type well DNW1.

In the shallow n-type well NW0 in the deep n-type well DNW0, the n-typediffusion tap ND0 is formed, while in the interlayer insulating film(not shown) formed over the substrate Sub (the deep n-type well DNW0),the coupling holes CNT1 are formed to reach the n-type diffusion tapND0. Likewise, in the shallow n-type well NW1 in the deep n-type wellDNW1, the n-type diffusion tap ND1 is formed, while in the interlayerinsulating film (not shown) formed over the substrate Sub (the deepn-type well DNW1), the coupling holes CNT1 are formed to reach then-type diffusion tap ND1. There is also formed the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusiontaps ND0 and ND1 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusiontap ND1 formed in the shallow n-type well NW1 in the deep n-type wellDNW1, and the coupling holes CNT2 reaching the interconnection M1 in thefirst layer which is electrically coupled to the n-type diffusion tapND0 formed in the shallow n-type well NW0 in the deep n-type well DNW0.The n-type diffusion tap ND1 formed in the shallow n-type well NW1 inthe deep n-type well DNW1 is electrically coupled to the n-typediffusion tap ND0 formed in the shallow n-type well NW0 in the deepn-type well DNW0 using the interconnection M2 in the second layer.

In the present third embodiment, it is assumed that the n-type diffusiontaps ND0 and ND1 are wired using an interconnection in a second orhigher order layer. However, in the case where layout using theinterconnection in the first layer is possible, the interconnection inthe first layer can also be used to wire the n-type diffusion taps ND0and ND1.

Thus, according to the present third embodiment, even when charge isaccumulated in the deep n-type well DNW1, the shallow n-type well NW1,and the shallow p-type well PW1, the charge can be discharged to anotherwell region such as the deep n-type well DNW0 only on the assumptionthat the potential of the deep n-type well DNW1 is the same as thepotential of the deep n-type well DNW0. This allows a reduction in thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 300 p and thenMIS 300 n which are each formed in the deep n-type well DNW1 to formthe inverter circuit INV1. In particular, when, e.g., the shallow p-typewell PW0 formed in the deep n-type well DNW0 is at a minus potentialrelative to the ground potential, i.e., when the power supply of theshallow n-type well NW1 formed in the deep n-type well DNW1 is the sameas the power supply of the shallow n-type well NW0 formed in the deepn-type well DNW0, and the power supply of the shallow p-type well PW1formed in the deep n-type well DNW1 is different from the power supplyof the shallow p-type well PW0 formed in the deep n-type well DNW0, thethird method in the present third embodiment serves as an effectivemeans.

Embodiment 4

In the present fourth embodiment, a description will be given of twoexamples (first and second examples) of a fourth method for preventing adielectric breakdown in the gate insulating film of a MIS in theforegoing third circuit (FIGS. 4( a) and 4(b) mentioned above). First,the first example of the fourth method will be described with referenceto FIGS. 17 to 19, and then the second example of the fourth method willbe described with reference to FIGS. 20 to 22. FIG. 17 is a circuitdiagram illustrating the first example of the fourth method forpreventing a dielectric breakdown in the gate insulating film of a MISaccording to the present fourth embodiment. FIG. 18 is aprincipal-portion cross-sectional view of the third circuit illustratingthe first example of the fourth method shown in FIG. 17 mentioned above.FIG. 19 is a principal-portion plan view of the third circuitillustrating the first example of the fourth method shown in FIG. 17mentioned above. FIG. 20 is a circuit diagram illustrating the secondexample of the fourth method for preventing a dielectric breakdown inthe gate insulating film of a MIS according to the present fourthembodiment. FIG. 21 is a principal-portion cross-sectional view of thethird circuit illustrating the second example of the fourth method shownin FIG. 20 mentioned above. FIG. 22 is a principal-portion plan view ofthe third circuit illustrating the second example of the fourth methodshown in FIG. 20 mentioned above.

First, the first example of the fourth method will be described.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 17, in the first example of the fourth method accordingto the present fourth embodiment, the p-type diffusion tap PD0 forpotential fixation is formed in the shallow p-type well PW0 in the deepn-type well DNW0, while in the shallow p-type well PW1 in the deepn-type well DNW1, a p-type diffusion tap PD1 for potential fixation isformed. The p-type diffusion tap. PD0 is coupled to the p-type diffusiontap PD1 using an interconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to wire the p-typediffusion tap PD0 to the p-type diffusion tap PD1, or an interconnectionin a layer higher in order than that. For example, in the case where thewiring of the p-type diffusion tap PD0 to the p-type diffusion tap PD1is performed using the interconnection in the second layer, the wiringof the inverter circuit INV0 formed in the deep n-type well DNW0 to theinverter circuit INV1 formed in the deep n-type well DNW1 is performedusing an interconnection in a second or higher order layer. In the casewhere the wiring of the p-type diffusion tap PD0 to the p-type diffusiontap PD1 is performed using the interconnection in the third layer, thewiring of the inverter circuit INV0 formed in the deep n-type well DNW0to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a third or higher order layer.

As shown in FIG. 18, in the third circuit (circuit in which wiring isprovided between the respective gate electrodes of the pMIS 300 p andthe nMIS 300 n which form the inverter circuit INV1 and the respectivedrain electrodes of the pMIS 200 p and the nMIS 200 n which form theinverter circuit INV0), a parasitic pn diode is formed by the wiring ofthe p-type diffusion tap PD0 to the p-type diffusion tap PD1. Becausethe parasitic pn diode is formed, and the respective gate electrodes ofthe nMIS 300 n and the pMIS 300 p which are formed in the deep n-typewell DNW1 are each in a floating state, the nMIS 300 n and the pMIS 300p are each brought into a conducting state. As a result, a dischargepath (or a discharge path in a direction reverse to that of thedischarge path) is formed which extends from the deep n-type well DNW1to the deep n-type well DNW0 via the shallow n-type well NW1, theshallow n-type diffusion tap ND1, the pMIS 300 p (the source electrodeSp thereof, the channel region thereof, and the drain electrode Dpthereof), the nMIS 300 n (the drain electrode Dn thereof, the channelregion thereof, and the source electrode Sn thereof), theinterconnection, the p-type diffusion tap PD0, and the shallow p-typewell PW0.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW1, the shallow n-typewell NW1, and the shallow p-type well PW1 in a manufacturing step usingplasma discharge such as, e.g., a dry etching step to another wellregion such as, e.g., the deep n-type well DNW0. As a result, thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0 is reduced. Therefore, it is possible to prevent adielectric breakdown in each of the gate insulating films of the pMIS300 p and the nMIS 300 n which are respectively formed in the shallown-type well NW1 and the shallow p-type well PW1 in the deep n-type wellDNW1.

FIG. 19 shows a principal-portion plan view of the p-type diffusion tapPD0 formed in the deep n-type well DNW0 and the p-type diffusion tap PD1formed in the deep n-type well DNW1.

In the shallow p-type well PW0 in the deep n-type well DNW0, the p-typediffusion tap PD0 is formed, while in the interlayer insulating film(not shown) formed over the substrate Sub (the deep n-type well DNW0),the coupling holes CNT1 are formed to reach the p-type diffusion tapPD0. Likewise, in the shallow p-type well PW1 in the deep n-type wellDNW1, the p-type diffusion tap PD1 is formed, while in the interlayerinsulating film (not shown) formed over the substrate Sub (the deepn-type well DNW1), the coupling holes CNT1 are formed to reach thep-type diffusion tap PD1. There is also formed the interconnection M1 inthe first layer which is electrically coupled to the p-type diffusiontaps PD0 and PD1 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the p-type diffusiontap PD1 formed in the shallow p-type well PW1 in the deep n-type wellDNW1, and the coupling holes CNT2 reaching the interconnection M1 in thefirst layer which is electrically coupled to the p-type diffusion tapPD0 formed in the shallow p-type well PW0 in the deep n-type well DNW0.The p-type diffusion tap PD1 formed in the shallow p-type well PW1 inthe deep n-type well DNW1 is electrically coupled to the p-typediffusion tap PD0 formed in the shallow p-type well PW0 in the deepn-type well DNW0 using the interconnection M2 in the second layer.

Next, the second example of the fourth method will be described.

In the second example of the fourth method also, a description is givenof the method for preventing a dielectric breakdown in the gateinsulating film of the pMIS 300 p or the nMIS 300 n forming the invertercircuit INV1, which occurs in the third circuit (FIGS. 4( a) and 4(b)mentioned above). The first and second examples of the fourth method aredifferent in that, in the first example, the p-type diffusion tap PD0formed in the shallow p-type well PW0 in the deep n-type well DNW0 iselectrically coupled to the p-type diffusion tap PD1 formed in theshallow p-type well PW1 in the deep n-type well DNW1, while in thesecond example, a shallow p-type well is further formed in the substrateSub, and a p-type diffusion tap for potential fixation which is formedin the shallow p-type well is electrically coupled to the p-typediffusion taps PD0 and PD1 mentioned above.

As shown in FIG. 20, in the second example of the fourth methodaccording to the present fourth embodiment, a p-type diffusion tap PD400for potential fixation is formed in a shallow p-type well PW400 which isformed in the substrate Sub, and the p-type diffusion tap 400 is furthercoupled to the p-type diffusion tap PD0 for potential fixation which isformed in the shallow p-type well PW0 in the deep n-type well DNW0 andto the p-type diffusion tap PD1 for potential fixation which is formedin the shallow p-type well PW1 in the deep n-type well DNW1 using aninterconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 n whichform the inverter circuit INV1 is performed using the interconnection inthe same layer as that of the interconnection used to wire the p-typediffusion tap PD0 to the p-type diffusion tap PD1, or an interconnectionin a layer higher in order than that. For example, in the case where thewiring of the p-type diffusion tap PD0 to the p-type diffusion tap PD1is performed using the interconnection in the second layer, the wiringof the inverter circuit INV0 formed in the deep n-type well DNW0 to theinverter circuit INV1 formed in the deep n-type well DNW1 is performedusing an interconnection in a second or higher order layer. In the casewhere the wiring of the p-type diffusion tap PD0 to the p-type diffusiontap PD1 is performed using the interconnection in the third layer, thewiring of the inverter circuit INV0 formed in the deep n-type well DNW0to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a third or higher order layer.

As shown in FIG. 21, in the third circuit (circuit in which wiring isprovided between the respective gate electrodes of the pMIS 300 p andthe nMIS 300 n forming the inverter circuit INV1 and the respectivedrain electrodes of the pMIS 200 p and the nMIS 200 n forming theinverter circuit INV0), the respective gate electrodes of the nMIS 300 nand the pMIS 300 p which are respectively formed in the shallow p-typewell PW1 and the shallow n-type well NW1 in the deep n-type well DNW1are each in a floating state so that the nMIS 300 n and the pMIS 300 pare each brought into a conducting state. As a result, a discharge pathis formed which extends from the deep n-type well DNW1 to the substrateSub via the shallow n-type well NW1, the n-type diffusion tap ND1, thepMIS 300 p (the source electrode Sp thereof, the channel region thereof,and the drain electrode Dp thereof), the nMIS 300 n (the drain electrodeDn thereof, the channel region thereof, and the source electrode Snthereof), the interconnection, the p-type diffusion tap PD400, and theshallow p-type well PW400. Likewise, the respective gate electrodes ofthe nMIS 200 n and the pMIS 200 p which are respectively formed in theshallow p-type well PW0 and the shallow n-type well NW0 in the deepn-type well DNW0 are each in a floating state so that the nMIS 200 n andthe pMIS 200 p are each brought into a conducting state. As a result, adischarge path is formed which extends from the deep n-type well DNW0 tothe substrate Sub via the shallow n-type well NW0, the n-type diffusiontap ND0, the pMIS 200 p (the source electrode Sp thereof, the channelregion thereof, and the drain electrode Dp thereof), the nMIS 200 n (thedrain electrode Dn thereof, the channel region thereof, and the sourceelectrode Sn thereof), the interconnection, the p-type diffusion tapPD400, and the shallow p-type well PW400.

In addition, a discharge path is formed which extends from the substrateSub to the deep n-type well DNW1 via the shallow p-type well PW400, thep-type diffusion tap PD400, the interconnection, the p-type diffusiontap PD1, and the shallow p-type well PW1. Likewise, a discharge path isformed which extends from the substrate Sub to the deep n-type well DNW0via the shallow p-type well PW400, the p-type diffusion tap PD400, theinterconnection, the p-type diffusion tap PD0, and the shallow p-typewell PW0.

The formation of the discharge paths mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW1, the shallow n-typewell NW1, and the shallow p-type well PW1 or the change accumulated inthe deep n-type well DNW0, the shallow n-type well NW0, and the shallowp-type well PW0 in a manufacturing step using plasma discharge such as,e.g., a dry etching step to the substrate Sub. As a result, thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0 is reduced. Therefore, it is possible to prevent adielectric breakdown in each of the gate insulating films of the pMIS300 p and the gate insulating film of the nMIS 300 n which arerespectively formed in the shallow n-type well NW1 and the shallowp-type well PW1 in the deep n-type well DNW1.

FIG. 22 shows a principal-portion plan view of the p-type diffusion tapPD0 formed in the deep n-type well DNW0, the p-type diffusion tap PD1formed in the deep n-type well DNW1, and the p-type diffusion tap PD400formed in the substrate Sub.

In addition to the p-type diffusion tap PD1 formed in the shallow p-typewell PW1 in the deep n-type well DNW1 and the p-type diffusion tap PD0formed in the shallow n-type well NW0 in the deep n-type well DNW0 whichare shown in FIG. 19 mentioned above, the p-type diffusion tap PD400 isformed in the shallow p-type well PW400 formed in the substrate Sub,similarly to the p-type diffusion taps PD0 and PD1. In the interlayerinsulating film (not shown) formed over the substrate Sub, the couplingholes CNT1 are formed to respectively reach the p-type diffusion tap PD1formed in the shallow p-type well PW1 in the deep n-type well DNW1, thep-type diffusion tap PD0 formed in the shallow n-type well NW0 in thedeep n-type well DNW0, and the p-type diffusion tap PD400 formed in theshallow p-type well PW400 in the substrate Sub. There is also formed theinterconnection M1 in the first layer which is electrically coupled tothe p-type diffusion tap PD1 formed in the shallow p-type well PW1 inthe deep n-type well DNW1, the p-type diffusion tap PD0 formed in theshallow n-type well NW0 in the deep n-type well DNW0, and the p-typediffusion tap PD400 formed in the shallow p-type well PW400 in thesubstrate Sub through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thecoupling holes CNT2 are formed to reach the interconnection M1 in thefirst layer which is electrically coupled to the p-type diffusion tapPD1 formed in the shallow p-type well PW1 in the deep n-type well DNW1,to the p-type diffusion tap PD0 formed in the shallow n-type well NW0 inthe deep n-type well DNW0, and to the p-type diffusion tap PD400 formedin the shallow p-type well PW400 in the substrate Sub. Through thecoupling holes CNT2, the p-type diffusion tap PD1 formed in the shallowp-type well PW1 in the deep n-type well DNW1, the p-type diffusion tapPD0 formed in the shallow n-type well NW0 in the deep n-type well DNW0,and the p-type diffusion tap PD400 formed in the shallow p-type wellPW400 in the substrate Sub are electrically coupled using theinterconnection M2 in the second layer.

In the present fourth embodiment, it is assumed that the wiring of thep-type diffusion taps PD0 and PD1 in the first example and the wiring ofthe p-type diffusion taps PD0, PD1, and PD400 in the second example areperformed using an interconnection in a second or higher order layer.However, in the case where layout using the interconnection in the firstlayer is possible, the interconnection in the first layer can also beused for the wiring.

Thus, according to the present fourth embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0, or in the deep n-type well DNW1, theshallow n-type well NW1, and the shallow p-type well PW1 due to a plasmacharge-up phenomenon in, e.g., a dry etching step, the charge can beeasily discharged to the substrate Sub to allow a reduction in thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0. As a result, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 300 p and thenMIS 300 n each formed the deep n-type well DNW1 to form the invertercircuit INV1. In particular, when the shallow p-type well PW0 formed inthe deep n-type well NDW0 and the shallow p-type well PW1 formed in thedeep n-type well DNW1 are at the same ground potential, i.e., when thepower supply of the shallow n-type well NW0 formed in the deep n-typewell DNW0 is different from the power supply of the shallow n-type wellNW1 formed in the deep n-type well DNW1, the fourth method in thepresent fourth embodiment serves as an effective means.

Embodiment 5

In the present fifth embodiment, a description will be given of a fifthmethod for preventing a dielectric breakdown in the gate insulating filmof a MIS in the foregoing third circuit (FIGS. 4( a) and 4(b) mentionedabove) with reference to FIGS. 23 to 25. FIG. 23 is a circuit diagramillustrating the fifth method for preventing a dielectric breakdown inthe gate insulating film of a MIS according to the present fifthembodiment. FIG. 24 is a principal-portion cross-sectional view of thethird circuit illustrating the fifth method shown in FIG. 23 mentionedabove. FIG. 25 is a principal-portion plan view of the third circuitillustrating the fifth method shown in FIG. 23 mentioned above.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 23, in the fifth method according to the present fifthembodiment, a shallow p-type well PW500 formed in the substrate Sub andan n-type diffusion layer formed in the shallow p-type well PW500 form apn diode Di500, and the cathode of the pn diode Di500 is coupled to then-type diffusion tap ND0 for potential fixation which is formed in theshallow n-type well NW0 in the deep n-type well DNW0 using aninterconnection in a second or higher order layer. In addition, ashallow p-type well PW501 formed in the substrate Sub and an n-typediffusion layer formed in the shallow p-type well PW501 form a pn diodeDi501, and the cathode of the pn diode Di501 is coupled to the n-typediffusion tap ND1 for potential fixation which is formed in the shallown-type well NW1 in the deep n-type well DNW1 using an interconnection ina second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to wire the n-typediffusion layer of the pn diode Di500 to the n-type diffusion tap ND0,and the interconnection used to wire the n-type diffusion layer of thepn diode Di501 to the n-type diffusion tap ND1, or an interconnection ina layer higher in order than that. For example, in the case where thewiring of the n-type diffusion layer of the pn diode Di500 to the n-typediffusion tap ND0, and the wiring of the n-type diffusion layer of thepn diode Di501 to the n-type diffusion tap ND1 are performed using theinterconnection in the second layer, the wiring of the inverter circuitINV0 formed in the deep n-type well DNW0 to the inverter circuit INV1formed in the deep n-type well DNW1 is performed using aninterconnection in a second or higher order layer. In the case where thewiring of the n-type diffusion layer of the pn diode Di500 to the n-typediffusion tap ND0, and the wiring of the n-type diffusion layer of thepn diode Di501 to the n-type diffusion tap ND1 are performed using theinterconnection in the third layer, the wiring of the inverter circuitINV0 formed in the deep n-type well DNW0 to the inverter circuit INV1formed in the deep n-type well DNW1 is performed using aninterconnection in a third or higher order layer.

As shown in FIG. 24, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), when the potential of the substrate Sub ishigher than the potential of the deep n-type well DNW0, the pn diodeDi500 forms a forward discharge path extending from the substrate Sub tothe deep n-type well DNW0 via the shallow p-type well PW500, an n-typediffusion layer DIn0, the interconnection, the n-type diffusion tap ND0,and the shallow n-type well NW0. When the potential of the substrate Subis lower than the potential of the deep n-type well DNW0, the pn diodeDi500 is in a reverse direction. For example, in a manufacturing stepusing plasma discharge such as a dry etching step, optical excitationdue to light emission or thermal excitation due to heat increases aleakage current in the reverse direction to form a discharge path.

Likewise, when the potential of the substrate Sub is higher than thepotential of the deep n-type well DNW1, the pn diode Di501 forms aforward discharge path extending from the substrate Sub to the deepn-type well DNW1 via the shallow p-type well PW501, an n-type diffusionlayer DIn1, the interconnection, the n-type diffusion tap ND1, and theshallow n-type well NW0. When the potential of the substrate Sub islower than the potential of the deep n-type well DNW1, the pn diodeDi501 is in a reverse direction. For example, in a manufacturing stepusing plasma discharge such as a dry etching step, optical excitationdue to light emission or thermal excitation due to heat increases aleakage current in the reverse direction to form a discharge path.

The formation of the discharge paths mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0 via the discharge pathmentioned above, and likewise allows discharge of the charge accumulatedin the deep n-type well DNW1, the shallow n-type well NW1, and theshallow p-type well PW1 via the discharge path mentioned above. As aresult, the potential difference between the deep n-type well DNW1 andthe deep n-type well DNW0 is reduced. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 300 p and the nMIS 300 n which are respectively formed in theshallow n-type well NW1 and the shallow p-type well PW1 in the deepn-type well DNW1.

FIG. 25 shows a principal-portion plan view of the pn diode Di500 formedin the substrate Sub, the n-type diffusion tap ND0 formed in the shallowp-type well NW0 in the deep n-type well DNW0, the pn diode Di501 formedin the substrate Sub, and the n-type diffusion tap ND1 formed in theshallow n-type well NW1 in the deep n-type well DNW1.

The n-type diffusion layer DIn0 is formed in the shallow p-type wellPW500 in the substrate Sub, while the n-type diffusion layer DIn1 isformed in the shallow p-type well PW501 in the substrate Sub. In theinterlayer insulating film (not shown) formed over the substrate Sub,the coupling holes CNT1 are formed to reach the n-type diffusion layersDIn0 and DIn1. In the shallow n-type well NW0 in the deep n-type wellDNW0, the n-type diffusion tap ND0 is formed, while in the shallown-type well NW1 in the deep n-type well DNW1, the n-type diffusion tapND1 is formed. In the interlayer insulating film (not shown) formed overthe substrate Sub (the deep n-type wells DNW0 and DNW1), the couplingholes CNT1 are formed to reach the n-type diffusion taps ND0 and ND1.There is also formed the interconnection M1 in the first layer which iselectrically coupled to the n-type diffusion taps ND0 and ND1 throughthe coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thecoupling holes CNT2 are formed to reach the interconnection M1 in thefirst layer which is electrically coupled to the n-type diffusion layerDIn0 formed in the shallow p-type well PW500 in the substrate Sub or tothe n-type diffusion layer DIn1 formed in the shallow p-type well PW501in the substrate Sub. Likewise, the coupling holes CNT2 are formed toreach the interconnection M1 in the first layer which is electricallycoupled to the n-type diffusion tap ND0 formed in the shallow n-typewell NW0 in the deep n-type well DNW0 or to the n-type diffusion tap ND1formed in the shallow n-type well NW1 in the deep n-type well DNW1. Then-type diffusion layer DIn0 formed in the shallow p-type well PW500 inthe substrate Sub is electrically coupled to the n-type diffusion tapND0 formed in the shallow n-type well NW0 in the deep n-type well DNW0coupled using the interconnection M2 in the second layer. Likewise, then-type diffusion layer DIn1 formed in the shallow p-type well PW501 inthe substrate Sub is electrically coupled to the n-type diffusion tapND1 formed in the shallow n-type well NW1 in the deep n-type well DNW1using the interconnection M2 in the second layer.

In the present fifth embodiment, it is assumed that the wiring of then-type diffusion tap ND0 to the cathode of the pn diode Di500, and thewiring of the n-type diffusion tap ND1 to the cathode of the pn diodeDi501 are performed using an interconnection in a second or higher orderlayer. However, in the case where layout using the interconnection inthe first layer is possible, the interconnection in the first layer canalso be used for the wiring.

Thus, according to the present fifth embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0 or in the deep n-type well DNW1, theshallow n-type well NW1, and the shallow p-type well PW1, the charge canbe easily discharged to the substrate Sub to allow a reduction in thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 300 p and thenMIS 300 n which are respectively formed in the shallow n-type well NW1and the shallow p-type well PW1 in the deep n-type well DNW1 to form theinverter circuit INV1. In particular, in the case where thesemiconductor device has, e.g., an analog leased ground and a back biasin combination, the shallow p-type well PW0 formed in the deep n-typewell DNW0 and the shallow p-type well PW1 formed in the deep n-type wellDNW1 are provided with grounds independent of each other, and a powersupply given to the shallow n-type well NW0 formed in the deep n-typewell DNW0 is interrupted for leakage current prevention, i.e., in thecase where the power supply of the shallow n-type well NW0 formed in thedeep n-type well DNW0 is different from the power supply of the shallown-type well NW1 formed in the deep n-type well DNW1, and the powersupply of the shallow p-type well PW0 formed in the deep n-type wellDNW0 is different from the power supply of the shallow p-type well PW1formed in the deep n-type well DNW1, the fifth method in the presentfifth embodiment serves as an effective means.

Embodiment 6

In the present sixth embodiment, a description will be given of twoexamples (first and second examples) of a sixth method for preventing adielectric breakdown in the gate insulating film of a MIS in theforegoing third circuit (FIGS. 4( a) and 4(b) mentioned above). First,the first example of the sixth method will be described with referenceto FIGS. 26 to 28, and then the second example of the sixth method willbe described with reference to FIGS. 29 and 30. FIG. 26 is a circuitdiagram illustrating the first example of the sixth method forpreventing a dielectric breakdown in the gate insulating film of a MISaccording to the present sixth embodiment. FIG. 27 is aprincipal-portion cross-sectional view of the third circuit illustratingthe first example of the sixth method shown in FIG. 26 mentioned above.FIG. 28 is a principal-portion plan view of the third circuitillustrating the first example of the sixth method shown in FIG. 26mentioned above. FIG. 29 is a circuit diagram illustrating the secondexample of the sixth method for preventing a dielectric breakdown in thegate insulating film of a MIS according to the present sixth embodiment.FIG. 30 is a principal-portion cross-sectional view of the third circuitillustrating the second example of the sixth method shown in FIG. 29mentioned above.

First, the first example of the sixth method will be described.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 26, in the first example of the sixth method accordingto the present sixth embodiment, a shallow p-type well PW600 formed inthe substrate Sub and an n-type diffusion layer formed in the shallowp-type well PW600 form a pn diode Di600. The cathode of the pn diodeDi600 and the n-type diffusion tap ND0 for potential fixation which isformed in the shallow n-type well NW0 in the deep n-type well DNW0 arecoupled using an interconnection in a second or higher order layer.

In the shallow p-type well PW601 formed in the substrate Sub, a p-typediffusion tap PD601 for potential fixation is formed. In the shallowp-type well PW1 in the deep n-type well DNW1, the p-type diffusion tapPD1 for potential fixation is formed. Further, the p-type diffusion tapPD600 and the p-type diffusion tap PD1 are coupled using aninterconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to wire the n-typediffusion layer of the pn diode Di600 to the n-type diffusion tap ND0,and the interconnection used to wire the p-type diffusion tap PD601 tothe p-type diffusion tap PD1, or an interconnection in a layer higher inorder than that. For example, in the case where the wiring of the n-typediffusion layer of the pn diode Di600 to the n-type diffusion tap ND0and the wiring of the p-type diffusion tap PD601 to the p-type diffusiontap PD1 are performed using the interconnection in the second layer, thewiring of the inverter circuit INV0 formed in the deep n-type well DNW0to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a second or higher order layer. Inthe case where the wiring of the n-type diffusion layer of the pn diodeDi600 to the n-type diffusion tap ND0 and the wiring of the p-typediffusion tap PD601 to the p-type diffusion tap PD1 are performed usingthe interconnection in the third layer, the wiring of the invertercircuit INV0 formed in the deep n-type well DNW0 to the inverter circuitINV1 formed in the deep n-type well DNW1 is performed using aninterconnection in a third or higher order layer.

As shown in FIG. 27, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), when the potential of the substrate Sub ishigher than the respective potentials of the deep n-type wells DNW0 andDNW1, the pn diode Di600 forms a forward discharge path extending fromthe substrate Sub to the deep n-type well DNW0 via the shallow p-typewell PW600, the n-type diffusion layer DIn0, the interconnection, then-type diffusion tap ND0, and the shallow n-type well NW0. In addition,a pn parasitic diode forms a discharge path extending from the substrateSub to the deep n-type well DNW1 via the shallow p-type well PW601, thep-type diffusion tap PD601, the interconnection, the p-type diffusiontap PD1, and the shallow p-type well PW1.

When the potential of the substrate Sub is lower than the respectivepotentials of the deep n-type wells DNW0 and DNW1, the pn diode Di600 isin a reverse direction. For example, in a manufacturing step usingplasma discharge such as a dry etching step, optical excitation due tolight emission or thermal excitation due to heat increases a leakagecurrent in the reverse direction to form a discharge path. Because therespective gate electrodes of the nMIS 300 n and the pMIS 300 p whichare respectively formed in the shallow p-type well PW1 and the shallown-type well NW1 in the deep n-type well DNW1 are each in a floatingstate, the nMIS 300 n and the pMIS 300 p are each brought into aconductive state. As a result, a discharge path is formed which extendsfrom the deep n-type well DNW1 to the substrate Sub via the shallown-type well NW1, the n-type diffusion tap ND1, the pMIS 300 p (thesource electrode Sp thereof, the channel region thereof, and the drainelectrode Dp thereof), the nMIS 300 n (the drain electrode Dn thereof,the channel region thereof, and the source electrode Sn thereof), theinterconnection, the p-type diffusion tap PD1, the p-type diffusion tapPD601, and the shallow p-type well PW601.

The formation of the discharge paths mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0 via the discharge pathmentioned above, and likewise allows discharge of the charge accumulatedin the deep n-type well DNW1, the shallow n-type well NW1, and theshallow p-type well PW1 via the discharge path mentioned above. As aresult, the potential difference between the deep n-type well DNW1 andthe deep n-type well DNW0 can be reduced. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 300 p and the nMIS 300 n which are respectively formed in theshallow n-type well NW1 and the shallow p-type well PW1 in the deepn-type well DNW1.

FIG. 28 shows a principal-portion plan view of the pn diode Di600 formedin the substrate Sub, the p-type diffusion tap PD601 formed in theshallow p-type well PW601 in the substrate Sub, the n-type diffusion tapND0 formed in the shallow n-type well NW0 in the deep n-type well DNW0,and the p-type diffusion tap PD1 formed in the shallow p-type well PW1in the deep n-type well DNW1.

The n-type diffusion layer DIn0 is formed in the shallow p-type wellPW600 formed in the substrate Sub, and the p-type diffusion tap PD601 isformed in the shallow p-type well PW601 formed in the substrate Sub. Inthe interlayer insulating film (not shown) formed over the substrateSub, the coupling holes CNT1 are formed to reach the n-type diffusionlayer DIn0 or the p-type diffusion tap PD601. The interconnection M1 inthe first layer is formed to be electrically coupled to the n-typediffusion layer DIn0 or the p-type diffusion tap PD601 through thecoupling holes CNT1. In the shallow n-type well NW0 in the deep n-typewell DNW0, the n-type diffusion tap ND0 is formed, while in the shallowp-type well PW1 in the deep n-type well DNW1, the p-type diffusion tapPD1 is formed. In the interlayer insulating film (not shown) formed onthe substrate (the deep n-type wells DNW0 and DNW1), the coupling holesCNT1 are formed to reach the n-type diffusion tap ND0 or the p-typediffusion tap PD1. The interconnection M1 in the first layer is formedto be electrically coupled to the n-type diffusion tap ND0 or the p-typediffusion tap PD1 through the coupling holes CNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusionlayer DIn0 formed in the shallow p-type well PW600 in the substrate Suband to the p-type diffusion tap PD601 formed in the shallow p-type wellPW601 in the substrate Sub, and the coupling holes CNT2 reaching theinterconnection M1 in the first layer which is electrically coupled tothe n-type diffusion tap ND0 formed in the shallow n-type well NW0 inthe deep n-type well DNW0 and to the p-type diffusion tap PD1 formed inthe shallow p-type well PW1 in the deep n-type well DNW1. The n-typediffusion layer DIn0 formed in the shallow p-type well PW600 in thesubstrate Sub is electrically coupled to the n-type diffusion tap ND0formed in the shallow n-type well NW0 in the deep n-type well DNW0 usingthe interconnection M2 in the second layer. Likewise, the p-typediffusion tap PD601 formed in the shallow p-type well PW601 in thesubstrate Sub is electrically coupled to the p-type diffusion tap PD1formed in the shallow p-type well PW1 in the deep n-type well DNW1 usingthe interconnection M2 in the second layer.

Next, the second example of the sixth method will be described.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 29, in the second example of the sixth method accordingto the present sixth embodiment, the p-type diffusion tap PD600 forpotential fixation is formed in the shallow p-type well PW600 in thesubstrate Sub, and the p-type diffusion tap PD0 for potential fixationis formed in the shallow p-type well PW0 in the deep n-type well DNW0.Further, the p-type diffusion tap PD600 and the p-type diffusion tap PD0are coupled using an interconnection in a second or higher order layer.

In addition, the shallow p-type well PW601 formed in the substrate Suband an n-type diffusion layer formed in the shallow p-type well PW601form a pn diode Di601. The cathode of the pn diode Di601 is coupled tothe n-type diffusion tap ND1 for potential fixation which is formed inthe shallow n-type well NW1 in the deep n-type well DNW1 using aninterconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 n whichform the inverter circuit INV1 is performed using the interconnection inthe same layer as that of the interconnection used to wire the p-typediffusion tap PD600 to the p-type diffusion tap PD0, and theinterconnection used to wire the n-type diffusion layer of the pn diodeDi601 to the n-type diffusion tap ND1, or an interconnection in a layerhigher in order than that. For example, in the case where the wiring ofthe p-type diffusion tap PD600 to the p-type diffusion tap PD0 and thewiring of the n-type diffusion layer of the pn diode Di601 to the n-typediffusion tap ND1 are performed using the interconnection in the secondlayer, the wiring of the inverter circuit INV0 formed in the deep n-typewell DNW0 to the inverter circuit INV1 formed in the deep n-type wellDNW1 is performed using an interconnection in a second or higher orderlayer. In the case where the wiring of the p-type diffusion tap PD600 tothe p-type diffusion tap PD0 and the wiring of the n-type diffusionlayer of the pn diode Di601 to the n-type diffusion tap ND1 areperformed using the interconnection in the third layer, the wiring ofthe inverter circuit INV0 formed in the deep n-type well DNW0 to theinverter circuit INV1 formed in the deep n-type well DNW1 is performedusing an interconnection in a third or higher order layer.

As shown in FIG. 30, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), when the potential of the substrate Sub ishigher than the respective potentials of the deep n-type wells DNW0 andDNW1, the pn diode Di600 forms a forward discharge path extending fromthe substrate Sub to the deep n-type well DNW1 via the shallow p-typewell PW601, the n-type diffusion layer DIn1, the interconnection, then-type diffusion tap ND1, and the shallow n-type well NW1. In addition,a pn parasitic diode forms a discharge path extending from the substrateSub to the deep n-type well DNW0 via the shallow p-type well PW600, thep-type diffusion tap PD600, the interconnection, the p-type diffusiontap PD0, and the shallow p-type well PW0.

When the potential of the substrate Sub is lower than the respectivepotentials of the deep n-type wells DNW0 and DNW1, the pn diode Di601 isin a reverse direction. For example, in a manufacturing step usingplasma discharge such as a dry etching step, optical excitation due tolight emission or thermal excitation due to heat increases a leakagecurrent in the reverse direction to form a discharge path. Because therespective gate electrodes of the nMIS 200 n and the pMIS 200 p whichare respectively formed in the shallow p-type well PW0 and the shallown-type well NW0 in the deep n-type well DNW0 are each in a floatingstate, the nMIS 200 n and the pMIS 200 p are each brought into aconductive state. As a result, a discharge path is formed which extendsfrom the deep n-type well DNW0 to the substrate Sub via the shallown-type well NW0, the p-type diffusion tap ND0, the pMIS 100 p (thesource electrode Sp thereof, the channel region thereof, and the drainelectrode Dp thereof), the nMIS 100 n (the drain electrode Dn thereof,the channel region thereof, and the source electrode Sn thereof), theinterconnection, the p-type diffusion tap PD600, and the shallow p-typewell PW600.

The formation of the discharge path mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0 via the discharge pathmentioned above, and likewise allows discharge of the charge accumulatedin the deep n-type well DNW1, the shallow n-type well NW1, and theshallow p-type well PW1 via the discharge path mentioned above. As aresult, the potential difference between the deep n-type well DNW1 andthe deep n-type well DNW0 is reduced. Therefore, it is possible toprevent a dielectric breakdown in each of the gate insulating films ofthe pMIS 300 p and the nMIS 300 n which are respectively formed in theshallow n-type well NW1 and the shallow p-type well PW1 in the deepn-type well DNW1.

In the present sixth embodiment, it is assumed that the n-type diffusiontap ND0 is wired to the cathode of the pn diode Di600 using aninterconnection in a second or higher order layer. However, in the casewhere layout using the interconnection in the first layer is possible,the interconnection in the first layer can also be used for the wiring.

Thus, according to the present sixth embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0, or in the deep n-type well DNW1, theshallow n-type well NW1, and the shallow p-type well PW1, the charge canbe easily discharged to the substrate Sub to allow a reduction in thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 300 p and thenMIS 300 n which are respectively formed in the shallow n-type well NW1and the shallow p-type well PW1 in the deep n-type well DNW1 to form theinverter circuit INV1. In particular, in the case where the pMIS 300 pand the nMIS 300 n which are respectively formed in the shallow n-typewell NW1 and the shallow p-type well PW1 in the deep n-type well DNW1form a digital circuit, the pMIS 200 p and the nMIS 200 n which arerespectively formed in the shallow n-type well NW0 and the shallowp-type well PW0 in the deep n-type well DNW0 form an analog circuit, andeach of the pMIS 300 p, the nMIS 300 n, the pMIS 200 p, and the nMIS 200n has a dedicated power supply or ground, i.e., in the case where thepower supply of the shallow n-type well NW0 formed in the deep n-typewell DNW0 is different from the power supply of the shallow n-type wellNW1 formed in the deep n-type well DNW1, and the power supply of theshallow p-type well PW0 formed in the deep n-type well DNW0 is differentfrom the power supply of the shallow p-type well PW1 formed in the deepn-type well DNW1, the sixth method in the present sixth embodimentserves as an effective means.

Embodiment 7

In the present seventh embodiment, a description will be given of twoexamples (first and second examples) of a seventh method for preventinga dielectric breakdown in the gate insulating film of a MIS in theforegoing third circuit (FIGS. 4( a) and 4(b) mentioned above). First,the first example of the seventh method will be described with referenceto FIGS. 31 to 33, and then the second example of the seventh methodwill be described with reference to FIGS. 34 to 36. FIG. 31 is a circuitdiagram illustrating the first example of the seventh method forpreventing a dielectric breakdown in the gate insulating film of a MISaccording to the present seventh embodiment. FIG. 32 is aprincipal-portion cross-sectional view of the third circuit illustratingthe first example of the seventh method shown in FIG. 31 mentionedabove. FIG. 33 is a principal-portion plan view of the third circuitillustrating the first example of the seventh method shown in FIG. 31mentioned above. FIG. 34 is a circuit diagram illustrating the secondexample of the seventh method for preventing a dielectric breakdown inthe gate insulating film of a MIS according to the present seventhembodiment. FIG. 35 is a principal-portion cross-sectional view of thethird circuit illustrating the second example of the seventh methodshown in FIG. 34 mentioned above. FIG. 36 is a principal-portioncross-sectional view of the third circuit illustrating the secondexample of the seventh method shown in FIG. 34 mentioned above.

First, the first example of the seventh method will be described.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n forming the inverter circuit INV1, a dielectricbreakdown has occurred.

As shown in FIG. 31, in the first example of the seventh methodaccording to the present seventh embodiment, the n-type diffusion tapND0 for potential fixation is formed in the shallow n-type well NW0 inthe deep n-type well DNW0, while the n-type diffusion tap ND1 forpotential fixation is formed in the shallow n-type well NW1 in the deepn-type well NW1. Further, between the n-type diffusion tap ND0 and then-type diffusion tap ND1, bidirectional diodes Di700 and Di701 areformed using an interconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to form thebidirectional diodes Di700 and Di 701, or an interconnection in a layerhigher in order than that. For example, in the case where theinterconnection in the second layer is used to form the bidirectionaldiodes Di700 and Di 701, the wiring of the inverter circuit INV0 formedin the deep n-type well DNW0 to the inverter circuit INV1 formed in thedeep n-type well DNW1 is performed using an interconnection in a secondor higher order layer. In the case where the interconnection in thethird layer is used to form the bidirectional diodes Di700 and Di 701,the wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a third or higher order layer.

As shown in FIG. 32, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), the n-type diffusion tap ND0 formed in theshallow n-type well NW0 in the deep n-type well DMW0 is wired to thecathode (the n-type diffusion layer DIn0 formed in a shallow n-type wellNW700 in the substrate Sub) of the bidirectional diode Di700 and to theanode (the p-type diffusion layer DIp1 formed in a shallow n-type wellNW701 in the substrate Sub) of the bidirectional diode Di701, and then-type diffusion tap ND1 formed in the shallow n-type well NW1 in thedeep n-type well DMW1 is wired to the anode (a p-type diffusion layerDIp0 formed in the shallow n-type well NW700 in the substrate Sub) ofthe bidirectional diode Di700 and to the cathode (the n-type diffusionlayer DIn1 formed in the shallow n-type well NW701 in the substrate Sub)of the bidirectional diode Di701. This forms a discharge path extendingfrom the deep n-type well DNW0 to the deep n-type well DNW1 via theshallow n-type well NW0, the n-type diffusion tap ND0, theinterconnection, the bidirectional diode Di701 (the n-type diffusionlayer DIn1, the shallow n-type well NW701, and the p-type diffusionlayer DIp1), the interconnection, the n-type diffusion tap ND1, and theshallow n-type well NW1. This also forms a discharge path extending fromthe deep n-type well DNW1 to the deep n-type well DNW0 via the shallown-type well NW1, the n-type diffusion tap ND1, the interconnection, thepn diode Di700 (the p-type diffusion layer DIp0, the shallow n-type wellNW700, and the n-type diffusion layer DIn0), the interconnection, then-type diffusion tap ND0, and the shallow n-type well NW0.

The formation of the discharge paths mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0 or the charge accumulated inthe deep n-type well DNW1, the shallow n-type well NW1, and the shallowp-type well PW1 via the discharge path mentioned above even when apotential difference occurs between the deep n-type well DNW1 and thedeep n-type well DNW0. As a result, the potential difference between thedeep n-type well DNW1 and the deep n-type well DNW0 is reduced.Therefore, it is possible to prevent a dielectric breakdown in each ofthe gate insulating films of the pMIS 300 p and the nMIS 300 n which arerespectively formed in the shallow n-type well NW1 and the shallowp-type well PW1 in the deep n-type well DNW1.

FIG. 33 shows a principal-portion plan view of the bidirectional diodesDi700 and Di701 formed in the substrate Sub, the n-type diffusion tapND0 formed in the deep n-type well DNW0, and the n-type diffusion tapND1 formed in the deep n-type well DNW1.

In the mutually different regions in the shallow n-type well NW700formed in the substrate Sub, the n-type diffusion layer DIn0 and thep-type diffusion layer DIp0 are formed (Di700). In the mutuallydifferent regions in the shallow n-type well NW701 formed in thesubstrate Sub, the n-type diffusion layer DIn1 and the p-type diffusionlayer DIp1 are formed (Di701). In the interlayer insulating film (notshown) formed over the substrate Sub, the coupling holes CNT1 are formedto individually reach the n-type diffusion layers DIn0 and DIn1 and thep-type diffusion layers DIp0 and DIp1. The n-type diffusion tap ND0 isformed in the shallow n-type well NW0 in the deep n-type well DNW0,while the n-type diffusion tap ND1 is formed in the shallow n-type wellNW1 in the deep n-type well DNW1. In the interlayer insulating film (notshown) formed over the substrate Sub (the deep n-type wells DNW0 andDNW1), the coupling holes CNT1 are formed to individually reach then-type diffusion taps ND0 and ND1, the n-type diffusion layers DIn0 andDIn1, and the p-type diffusion layers DIp0 and DIp1. The interconnectionM1 in the first layer is formed to be electrically coupled to the n-typediffusion taps ND0 and ND1, the n-type diffusion layers DIn0 and DIn1,and the p-type diffusion layers DIp0 and DIp1 through the coupling holesCNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusionlayer DIn0 and the p-type diffusion layer DIp0 each formed in theshallow n-type well NW700 in the substrate Sub and to the n-typediffusion layer DIn1 and the p-type diffusion layer DIp1 each formed inthe shallow n-type well NW701 in the substrate Sub, and the couplingholes CNT2 reaching the interconnection M1 in the first layer which iselectrically coupled to the n-type diffusion tap ND0 and the n-typediffusion tap ND1 which are respectively formed in the shallow n-typewell NW0 in the deep n-type well DNW0 and the shallow n-type well NW1 inthe deep n-type well DNW1. The p-type diffusion layer DIp1 (thebidirectional diode Di701) formed in the shallow n-type well NW701 inthe substrate Sub, the n-type diffusion layer DIn0 (the bidirectionaldiode Di700) formed in the shallow n-type well NW700 in the substrateSub, and the n-type diffusion tap ND0 formed in the shallow n-type wellNW0 in the deep n-type well DNW0 are electrically coupled using theinterconnection M2 in the second layer. The p-type diffusion layer DIp0(the bidirectional diode Di700) formed in the shallow n-type well NW700in the substrate Sub, the n-type diffusion layer DIn1 (the bidirectionaldiode Di701) formed in the shallow n-type well NW701 in the substrateSub, and the n-type diffusion tap ND1 in the shallow n-type well NW1formed in the deep n-type well DNW1 are electrically coupled using theinterconnection M2 in the second layer.

Next, the second example of the seventh method will be described.

As described above, the third circuit (FIGS. 4( a) and 4(b) mentionedabove) includes the inverter circuit INV0 formed in the deep n-type wellDNW0, and the inverter circuit INV1 formed in the deep n-type well DNW1.The respective gate electrodes of the pMIS 300 p and the nMIS 300 nwhich form the inverter circuit INV1 are electrically coupled to therespective drain electrodes of the pMIS 200 p and the nMIS 200 n whichform the inverter circuit INV0. In the gate insulating film of the pMIS300 p or the nMIS 300 n which form the inverter circuit INV1, adielectric breakdown has occurred.

As shown in FIG. 34, in the second example of the seventh methodaccording to the present seventh embodiment, the p-type diffusion tapPD0 for potential fixation is formed in the shallow p-type well PW0 inthe deep n-type well DNW0, and the p-type diffusion tap PD1 forpotential fixation is formed in the shallow p-type well PW1 in the deepn-type well DNW1. Further, the bidirectional diodes Di700 and Di701 areformed between the p-type diffusion tap PD0 and the p-type diffusion tapPD1 using an interconnection in a second or higher order layer.

The wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 and the inverter circuit INV1 formed in the deep n-type well DNW1,i.e., the wiring of the respective drain electrodes of the pMIS 200 pand the nMIS 200 n which form the inverter circuit INV0 to therespective gate electrodes of the pMIS 300 p and the nMIS 300 p whichform the inverter circuit INV1 is performed using an interconnection inthe same layer as that of the interconnection used to form thebidirectional diodes Di700 and Di 701, or an interconnection in a layerhigher in order than that. For example, in the case where theinterconnection in the second layer is used to form the bidirectionaldiodes Di700 and Di 701, the wiring of the inverter circuit INV0 formedin the deep n-type well DNW0 to the inverter circuit INV1 formed in thedeep n-type well DNW1 is performed using an interconnection in a secondor higher order layer. In the case where the interconnection in thethird layer is used to form the bidirectional diodes Di700 and Di 701,the wiring of the inverter circuit INV0 formed in the deep n-type wellDNW0 to the inverter circuit INV1 formed in the deep n-type well DNW1 isperformed using an interconnection in a third or higher order layer.

As shown in FIG. 35, in the third circuit (circuit in which wiring isprovided between the respective drain electrodes of the pMIS 200 p andthe nMIS 200 n which form the inverter circuit INV0 and the respectivegate electrodes of the pMIS 300 p and the nMIS 300 n which form theinverter circuit INV1), the p-type diffusion tap PD0 formed in theshallow p-type well PW0 in the deep n-type well DMW0 is wired to thecathode (the n-type diffusion layer DIn0 formed in the shallow n-typewell NW700 in the substrate Sub) of the bidirectional diode Di700 and tothe anode (the p-type diffusion layer DIp1 formed in the shallow n-typewell NW701 in the substrate Sub) of the bidirectional diode Di701, andthe p-type diffusion tap PD1 formed in the shallow p-type well PW1 inthe deep n-type well DMW1 is wired to the cathode (the n-type diffusionlayer DIn1 formed in the shallow n-type well NW701 in the substrate Sub)of the bidirectional diode Di701 and to the anode (the p-type diffusionlayer DIp0 formed in the shallow n-type well NW700 in the substrate Sub)of the bidirectional diode Di700. This forms a discharge path extendingfrom the deep n-type well DNW0 to the deep n-type well DNW1 via theshallow p-type well PW0, the p-type diffusion tap PD0, theinterconnection, the pn diode Di701 (the p-type diffusion layer DIp1,the shallow n-type well NW701, and the n-type diffusion layer DIn1), theinterconnection, the p-type diffusion tap PD1, and the shallow p-typewell PW1. This also forms a discharge path extending from the deepn-type well DNW1 to the deep n-type well DNW0 via the shallow p-typewell PW1, the p-type diffusion tap PD1, the interconnection, the pndiode Di700 (the p-type diffusion layer DIp0, the shallow n-type wellNW700, and the n-type diffusion layer DIn0), the interconnection, thep-type diffusion tap PD0, and the shallow p-type well PW0.

The formation of the discharge paths mentioned above allows discharge ofthe charge accumulated in the deep n-type well DNW0, the shallow n-typewell NW0, and the shallow p-type well PW0 or the charge accumulated inthe deep n-type well DNW1, the shallow n-type well NW1, and the shallowp-type well PW1 via the discharge path mentioned above even when apotential difference occurs between the deep n-type well DNW1 and thedeep n-type well DNW0. As a result, the potential difference between thedeep n-type well DNW1 and the deep n-type well DNW0 is reduced.Therefore, it is possible to prevent a dielectric breakdown in each ofthe gate insulating films of the pMIS 300 p and the nMIS 300 n which arerespectively formed in the shallow n-type well NW1 and the shallowp-type well PW1 in the deep n-type well DNW1.

FIG. 36 shows a principal-portion plan view of the bidirectional diodesDi700 and Di701 formed in the substrate Sub, the n-type diffusion tapND0 formed in the deep n-type well DNW0, and the n-type diffusion tapND1 formed in the deep n-type well DNW1.

In the mutually different regions in the shallow n-type well NW700formed in the substrate Sub, the n-type diffusion layer DIn0 and thep-type diffusion layer DIp0 are formed (Di700). In the mutuallydifferent regions in the shallow n-type well NW701 formed in thesubstrate Sub, the n-type diffusion layer DIn1 and the p-type diffusionlayer DIp1 are formed (Di701). In the interlayer insulating film (notshown) formed over the substrate Sub, the coupling holes CNT1 are formedto individually reach the n-type diffusion layers DIn0 and DIn1 and thep-type diffusion layers DIp0 and DIp1. The p-type diffusion tap PD0 isformed in the shallow p-type well PW0 in the deep n-type well DNW0,while the p-type diffusion tap PD1 is formed in the shallow p-type wellPW1 in the deep n-type well DNW1. In the interlayer insulating film (notshown) formed over the substrate Sub (the deep n-type wells DNW0 andDNW1), the coupling holes CNT1 are formed to individually reach thep-type diffusion taps PD0 and PD1, the n-type diffusion layers DIn0 andDIn1, and the p-type diffusion layers DIp0 and DIp1. The interconnectionM1 in the first layer is formed to be electrically coupled to the p-typediffusion taps PD0 and PD1, the n-type diffusion layers DIn0 and DIn1,and the p-type diffusion layers DIp0 and DIp1 through the coupling holesCNT1.

Further, in the interlayer insulating film (not shown) formed over thesubstrate Sub to cover the interconnection M1 in the first layer, thereare formed the coupling holes CNT2 reaching the interconnection M1 inthe first layer which is electrically coupled to the n-type diffusionlayer DIn0 and the p-type diffusion layer DIp0 each formed in theshallow n-type well NW700 in the substrate Sub and to the n-typediffusion layer DIn and the p-type diffusion layer DIp1 each formed inthe shallow n-type well NW701 in the substrate Sub, and the couplingholes CNT2 reaching the interconnection M1 in the first layer which iselectrically coupled to the p-type diffusion tap PD0 and the p-typediffusion tap PD1 which are respectively formed in the shallow p-typewell PW0 in the deep n-type well DNW0 and the shallow p-type well PW1 inthe deep n-type well DNW1. The n-type diffusion layer DIn1 (thebidirectional diode Di701) formed in the shallow n-type well NW701 inthe substrate Sub, the n-type diffusion layer DIn0 (the bidirectionaldiode Di700) formed in the shallow n-type well NW700 in the substrateSub, and the p-type diffusion tap PD0 formed in the shallow p-type wellPW0 in the deep n-type well DNW0 are electrically coupled using theinterconnection M2 in the second layer. The p-type diffusion layer DIp0(the bidirectional diode Di700) formed in the shallow n-type well NW700in the substrate Sub, the n-type diffusion layer DIn1 (the bidirectionaldiode Di701) formed in the shallow n-type well NW701 in the substrateSub, and the p-type diffusion tap PD1 in the shallow p-type well PW1formed in the deep n-type well DNW1 are electrically coupled using theinterconnection M2 in the second layer.

In the present seventh embodiment, it is assumed that the wiring of then-type diffusion tap ND0 to the cathode of the pn diode Di700 and to theanode of the pn diode Di701 and the wiring of the n-type diffusion tapND1 to the anode of the pn diode Di700 and to the cathode of the pndiode Di701 in the first example, and the wiring of the p-type diffusiontap PD0 to the cathode of the pn diode 700 and to the anode of the pndiode Di701 and the wiring of the p-type diffusion tap PD1 to the anodeof the pn diode 700 and to the cathode of the pn diode 701 are eachperformed using an interconnection in a second or higher order layer.However, in the case where layout using the interconnection in the firstlayer is possible, the interconnection in the first layer can also beused for the wiring.

Thus, according to the present seventh embodiment, even when charge isaccumulated in the deep n-type well DNW0, the shallow n-type well NW0,and the shallow p-type well PW0, or in the deep n-type well DNW1, theshallow n-type well NW1, and the shallow p-type well PW1, the charge canbe easily discharged to another well region to allow a reduction in thepotential difference between the deep n-type well DNW1 and the deepn-type well DNW0. Therefore, it is possible to prevent a dielectricbreakdown in each of the gate insulating films of the pMIS 300 p and thenMIS 300 n which are respectively formed in the shallow n-type well NW1and the shallow p-type well PW1 in the deep n-type well DNW1 to form theinverter circuit INV1. In particular, in the case where the shallowp-type well PW0 and the shallow n-type well NW0 each formed in the deepn-type well DNW0 form an analog circuit, and have respective particularpower supplies or ground potentials, and the shallow p-type well PW1 andthe shallow n-type well N1 each formed in the deep n-type well DNW1 formanother analog circuit, and have respective particular power supplies orground potential which are different from the power supplies or theground potentials applied to the shallow p-type well PW0 and the shallown-type well NW0 each formed in the deep n-type well DNW0, i.e., in thecase where the power supply of the shallow p-type well PW0 formed in thedeep n-type well DNW0 is different from the power supply of the shallowp-type well PW1 formed in the deep n-type well DNW1, and the powersupply of the shallow n-type well NW0 formed in the deep n-type wellDNW0 is different from the power supply of the shallow n-type well NW1formed in the deep n-type well DNW1, the seventh method in the presentseventh embodiment serves as an effective means.

While the invention achieved by the present inventors has been describedspecifically based on the embodiments of the invention, it will beeasily appreciated that the present invention is not limited to theembodiments described above, and various changes and modification can bemade therein without departing from the gist thereof.

The present invention provides a technology which is effective whenapplied to a semiconductor device having a triple well structure adoptedto, e.g., a versatile SOC product.

1-5. (canceled)
 6. A semiconductor device comprising: a substrate of afirst conductivity type; a deep well of a second conductivity typedifferent from the first conductivity type which is formed in thesubstrate; a first shallow well of the first conductivity type and asecond shallow well of the second conductivity type which are formed inmutually different regions in the substrate; a first field effecttransistor of the second conductivity type which is formed in the firstshallow well; a second field effect transistor of the first conductivitytype which is formed in the second shallow well; a third shallow well ofthe first conductivity type and a fourth shallow well of the secondconductivity type which are formed in mutually different regions in thedeep well; a third field effect transistor of the second conductivitytype which is formed in the third shallow well; a fourth field effecttransistor of the first conductivity type which is formed in the fourthshallow well; a sixth shallow well of the first conductivity type whichis formed in a region different from respective regions in the substratewhere the deep well, the first shallow well, and the second shallow wellare formed; and a diffusion layer of the second conductivity type whichis formed in the sixth shallow well, wherein the diffusion layer iswired to a fourth diffusion tap of the second conductivity type which isformed in the fourth shallow well using an interconnection in an n-thlayer, and wherein respective gate electrodes of the third field effecttransistor the fourth field effect transistor are wired to respectivedrain electrodes of the first field effect transistor and the secondfield effect transistor using an interconnection in an n-th or higherorder layer.
 7. A semiconductor device according to claim 6, wherein thefirst and second field effect transistors form a digital circuit, andthe third and fourth field effect transistors form an analog circuit. 8.A semiconductor device according to claim 6, wherein a power supply ofthe first shallow well and a power supply of the third shallow well aredifferent from each other, and a power supply of the second shallow welland a power supply of the fourth shallow well are different from eachother.
 9. A semiconductor device according to claim 6, wherein theinterconnection in the n-th layer is an interconnection in a secondlayer.
 10. A semiconductor device according to claim 6, wherein thefirst field effect transistor and the second field effect transistorform an inverter circuit, and the third field effect transistor and thefourth field effect transistor form another inverter circuit. 11-38.(canceled)